diff --git a/configure.ac b/configure.ac
old mode 100644
new mode 100755
index edebfc7..a72a612
--- a/configure.ac
+++ b/configure.ac
@@ -148,6 +148,7 @@
     curl_ssl_msg="no      (--with-{ssl,gnutls,nss,polarssl,mbedtls,cyassl,axtls,winssl,darwinssl} )"
     curl_ssh_msg="no      (--with-libssh2)"
    curl_zlib_msg="no      (--with-zlib)"
+ curl_brotli_msg="no      (--with-brotli)"
     curl_gss_msg="no      (--with-gssapi)"
 curl_tls_srp_msg="no      (--enable-tls-srp)"
     curl_res_msg="default (--enable-ares / --enable-threaded-resolver)"
@@ -165,7 +166,7 @@
   curl_mtlnk_msg="no      (--with-libmetalink)"
     curl_psl_msg="no      (--with-libpsl)"
 
-    init_ssl_msg=${curl_ssl_msg}
+    ssl_backends=
 
 dnl
 dnl Save some initial values the user might have provided
@@ -183,9 +184,6 @@
 
 dnl Checks for programs.
 
-dnl Our curl_off_t internal and external configure settings
-CURL_CONFIGURE_CURL_OFF_T
-
 dnl This defines _ALL_SOURCE for AIX
 CURL_CHECK_AIX_ALL_SOURCE
 
@@ -354,6 +352,7 @@
 CURL_CHECK_WIN32_LARGEFILE
 
 CURL_MAC_CFLAGS
+CURL_SUPPORTS_BUILTIN_AVAILABLE
 
 dnl ************************************************************
 dnl switch off particular protocols
@@ -978,6 +977,94 @@
 AC_SUBST(ZLIB_LIBS)
 
 dnl **********************************************************************
+dnl Check for the presence of BROTLI decoder libraries and headers
+dnl **********************************************************************
+
+dnl Brotli project home page: https://github.com/google/brotli
+
+dnl Default to compiler & linker defaults for BROTLI files & libraries.
+OPT_BROTLI=off
+AC_ARG_WITH(brotli,dnl
+AC_HELP_STRING([--with-brotli=PATH],[Where to look for brotli, PATH points to the BROTLI installation; when possible, set the PKG_CONFIG_PATH environment variable instead of using this option])
+AC_HELP_STRING([--without-brotli], [disable BROTLI]),
+  OPT_BROTLI=$withval)
+
+if test X"$OPT_BROTLI" != Xno; then
+  dnl backup the pre-brotli variables
+  CLEANLDFLAGS="$LDFLAGS"
+  CLEANCPPFLAGS="$CPPFLAGS"
+  CLEANLIBS="$LIBS"
+
+  case "$OPT_BROTLI" in
+  yes)
+    dnl --with-brotli (without path) used
+    CURL_CHECK_PKGCONFIG(libbrotlidec)
+
+    if test "$PKGCONFIG" != "no" ; then
+      LIB_BROTLI=`$PKGCONFIG --libs-only-l libbrotlidec`
+      LD_BROTLI=`$PKGCONFIG --libs-only-L libbrotlidec`
+      CPP_BROTLI=`$PKGCONFIG --cflags-only-I libbrotlidec`
+      version=`$PKGCONFIG --modversion libbrotlidec`
+      DIR_BROTLI=`echo $LD_BROTLI | $SED -e 's/-L//'`
+    fi
+
+    ;;
+  off)
+    dnl no --with-brotli option given, just check default places
+    ;;
+  *)
+    dnl use the given --with-brotli spot
+    PREFIX_BROTLI=$OPT_BROTLI
+    ;;
+  esac
+
+  dnl if given with a prefix, we set -L and -I based on that
+  if test -n "$PREFIX_BROTLI"; then
+    LIB_BROTLI="-lbrotlidec"
+    LD_BROTLI=-L${PREFIX_BROTLI}/lib$libsuff
+    CPP_BROTLI=-I${PREFIX_BROTLI}/include
+    DIR_BROTLI=${PREFIX_BROTLI}/lib$libsuff
+  fi
+
+  LDFLAGS="$LDFLAGS $LD_BROTLI"
+  CPPFLAGS="$CPPFLAGS $CPP_BROTLI"
+  LIBS="$LIB_BROTLI $LIBS"
+
+  AC_CHECK_LIB(brotlidec, BrotliDecoderDecompress)
+
+  AC_CHECK_HEADERS(brotli/decode.h,
+    curl_brotli_msg="enabled (libbrotlidec)"
+    HAVE_BROTLI=1
+    AC_DEFINE(HAVE_BROTLI, 1, [if BROTLI is in use])
+    AC_SUBST(HAVE_BROTLI, [1])
+  )
+
+  if test X"$OPT_BROTLI" != Xoff &&
+     test "$HAVE_BROTLI" != "1"; then
+    AC_MSG_ERROR([BROTLI libs and/or directories were not found where specified!])
+  fi
+
+  if test "$HAVE_BROTLI" = "1"; then
+    if test -n "$DIR_BROTLI"; then
+       dnl when the brotli shared libs were found in a path that the run-time
+       dnl linker doesn't search through, we need to add it to LD_LIBRARY_PATH
+       dnl to prevent further configure tests to fail due to this
+
+       if test "x$cross_compiling" != "xyes"; then
+         LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$DIR_BROTLI"
+         export LD_LIBRARY_PATH
+         AC_MSG_NOTICE([Added $DIR_BROTLI to LD_LIBRARY_PATH])
+       fi
+    fi
+  else
+    dnl no brotli, revert back to clean variables
+    LDFLAGS=$CLEANLDFLAGS
+    CPPFLAGS=$CLEANCPPFLAGS
+    LIBS=$CLEANLIBS
+  fi
+fi
+
+dnl **********************************************************************
 dnl Check for LDAP
 dnl **********************************************************************
 
@@ -1336,6 +1423,41 @@
   CPPFLAGS="$save_CPPFLAGS"
 fi
 
+build_libstubgss=no
+if test x"$want_gss" = "xyes"; then
+  build_libstubgss=yes
+fi
+
+AM_CONDITIONAL(BUILD_STUB_GSS, test "x$build_libstubgss" = "xyes")
+
+dnl -------------------------------------------------------------
+dnl parse --with-default-ssl-backend so it can be validated below
+dnl -------------------------------------------------------------
+
+DEFAULT_SSL_BACKEND=no
+VALID_DEFAULT_SSL_BACKEND=
+AC_ARG_WITH(default-ssl-backend,
+AC_HELP_STRING([--with-default-ssl-backend=NAME],[Use NAME as default SSL backend])
+AC_HELP_STRING([--without-default-ssl-backend],[Use implicit default SSL backend]),
+  [DEFAULT_SSL_BACKEND=$withval])
+case "$DEFAULT_SSL_BACKEND" in
+  no)
+    dnl --without-default-ssl-backend option used
+    ;;
+  default|yes)
+    dnl --with-default-ssl-backend option used without name
+    AC_MSG_ERROR([The name of the default SSL backend is required.])
+    ;;
+  *)
+    dnl --with-default-ssl-backend option used with name
+    AC_SUBST(DEFAULT_SSL_BACKEND)
+    dnl needs to be validated below
+    VALID_DEFAULT_SSL_BACKEND=no
+    ;;
+esac
+
+dnl **********************************************************************
+
 dnl -------------------------------------------------
 dnl check winssl option before other SSL libraries
 dnl -------------------------------------------------
@@ -1347,13 +1469,15 @@
   OPT_WINSSL=$withval)
 
 AC_MSG_CHECKING([whether to enable Windows native SSL/TLS (Windows native builds only)])
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_WINSSL" != xno; then
+  ssl_msg=
   if test "x$OPT_WINSSL" != "xno"  &&
      test "x$curl_cv_native_windows" = "xyes"; then
     AC_MSG_RESULT(yes)
     AC_DEFINE(USE_SCHANNEL, 1, [to enable Windows native SSL/TLS support])
     AC_SUBST(USE_SCHANNEL, [1])
-    curl_ssl_msg="enabled (Windows-native)"
+    ssl_msg="Windows-native"
+    test schannel != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
     WINSSL_ENABLED=1
     # --with-winssl implies --enable-sspi
     AC_DEFINE(USE_WINDOWS_SSPI, 1, [to enable SSPI support])
@@ -1363,6 +1487,7 @@
   else
     AC_MSG_RESULT(no)
   fi
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 else
   AC_MSG_RESULT(no)
 fi
@@ -1374,18 +1499,20 @@
   OPT_DARWINSSL=$withval)
 
 AC_MSG_CHECKING([whether to enable Apple OS native SSL/TLS])
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_DARWINSSL" != xno; then
   if test "x$OPT_DARWINSSL" != "xno" &&
      test -d "/System/Library/Frameworks/Security.framework"; then
     AC_MSG_RESULT(yes)
     AC_DEFINE(USE_DARWINSSL, 1, [to enable Apple OS native SSL/TLS support])
     AC_SUBST(USE_DARWINSSL, [1])
-    curl_ssl_msg="enabled (Apple OS-native)"
+    ssl_msg="Apple OS-native"
+    test darwinssl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
     DARWINSSL_ENABLED=1
     LDFLAGS="$LDFLAGS -framework CoreFoundation -framework Security"
   else
     AC_MSG_RESULT(no)
   fi
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 else
   AC_MSG_RESULT(no)
 fi
@@ -1403,7 +1530,10 @@
 AC_HELP_STRING([--without-ssl], [disable OpenSSL]),
   OPT_SSL=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg" && test X"$OPT_SSL" != Xno; then
+if test -z "$ssl_backends" -o "x$OPT_SSL" != xno &&
+   test X"$OPT_SSL" != Xno; then
+  ssl_msg=
+
   dnl backup the pre-ssl variables
   CLEANLDFLAGS="$LDFLAGS"
   CLEANCPPFLAGS="$CPPFLAGS"
@@ -1584,7 +1714,8 @@
       dnl Have the libraries--check for OpenSSL headers
       AC_CHECK_HEADERS(openssl/x509.h openssl/rsa.h openssl/crypto.h \
                        openssl/pem.h openssl/ssl.h openssl/err.h,
-        curl_ssl_msg="enabled (OpenSSL)"
+        ssl_msg="OpenSSL"
+	test openssl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
         OPENSSL_ENABLED=1
         AC_DEFINE(USE_OPENSSL, 1, [if OpenSSL is in use]))
 
@@ -1598,16 +1729,13 @@
            test $ac_cv_header_crypto_h = yes &&
            test $ac_cv_header_ssl_h = yes; then
           dnl three matches
-          curl_ssl_msg="enabled (OpenSSL)"
+          ssl_msg="OpenSSL"
           OPENSSL_ENABLED=1
         fi
       fi
     fi
 
-    if test X"$OPENSSL_ENABLED" = X"1"; then
-       dnl is there a pkcs12.h header present?
-       AC_CHECK_HEADERS(openssl/pkcs12.h)
-    else
+    if test X"$OPENSSL_ENABLED" != X"1"; then
        LIBS="$CLEANLIBS"
     fi
 
@@ -1649,7 +1777,7 @@
         AC_MSG_RESULT([yes])
         AC_DEFINE_UNQUOTED(HAVE_BORINGSSL, 1,
                            [Define to 1 if using BoringSSL.])
-        curl_ssl_msg="enabled (BoringSSL)"
+        ssl_msg="BoringSSL"
     ],[
         AC_MSG_RESULT([no])
     ])
@@ -1665,7 +1793,7 @@
       AC_MSG_RESULT([yes])
       AC_DEFINE_UNQUOTED(HAVE_LIBRESSL, 1,
         [Define to 1 if using libressl.])
-      curl_ssl_msg="enabled (libressl)"
+      ssl_msg="libressl"
     ],[
       AC_MSG_RESULT([no])
     ])
@@ -1685,6 +1813,7 @@
     CURL_CHECK_OPENSSL_API
   fi
 
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
 dnl **********************************************************************
@@ -1746,7 +1875,8 @@
 AC_HELP_STRING([--without-gnutls], [disable GnuTLS detection]),
   OPT_GNUTLS=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_GNUTLS" != xno; then
+  ssl_msg=
 
   if test X"$OPT_GNUTLS" != Xno; then
 
@@ -1820,7 +1950,8 @@
        AC_SUBST(USE_GNUTLS, [1])
        GNUTLS_ENABLED=1
        USE_GNUTLS="yes"
-       curl_ssl_msg="enabled (GnuTLS)"
+       ssl_msg="GnuTLS"
+       test gnutls != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
        ],
        [
          LIBS="$CLEANLIBS"
@@ -1835,7 +1966,7 @@
           dnl linker doesn't search through, we need to add it to
           dnl LD_LIBRARY_PATH to prevent further configure tests to fail
           dnl due to this
-          if test "x$cross_compiling" != "xyes"; then 
+          if test "x$cross_compiling" != "xyes"; then
             LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$gtlslib"
             export LD_LIBRARY_PATH
             AC_MSG_NOTICE([Added $gtlslib to LD_LIBRARY_PATH])
@@ -1848,6 +1979,7 @@
 
   fi dnl GNUTLS not disabled
 
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
 dnl ---
@@ -1905,7 +2037,8 @@
 AC_HELP_STRING([--without-polarssl], [disable PolarSSL detection]),
   OPT_POLARSSL=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_POLARSSL" != xno; then
+  ssl_msg=
 
   if test X"$OPT_POLARSSL" != Xno; then
 
@@ -1923,7 +2056,8 @@
          AC_SUBST(USE_POLARSSL, [1])
          POLARSSL_ENABLED=1
          USE_POLARSSL="yes"
-         curl_ssl_msg="enabled (PolarSSL)"
+         ssl_msg="PolarSSL"
+	 test polarssl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
         ])
     fi
 
@@ -1949,7 +2083,8 @@
        AC_SUBST(USE_POLARSSL, [1])
        POLARSSL_ENABLED=1
        USE_POLARSSL="yes"
-       curl_ssl_msg="enabled (PolarSSL)"
+       ssl_msg="PolarSSL"
+       test polarssl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
        ],
        [
          CPPFLAGS=$_cppflags
@@ -1977,6 +2112,7 @@
 
   fi dnl PolarSSL not disabled
 
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
 dnl ----------------------------------------------------
@@ -1992,7 +2128,8 @@
 AC_HELP_STRING([--without-mbedtls], [disable mbedTLS detection]),
   OPT_MBEDTLS=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_MBEDTLS" != xno; then
+  ssl_msg=
 
   if test X"$OPT_MBEDTLS" != Xno; then
 
@@ -2010,7 +2147,8 @@
          AC_SUBST(USE_MBEDTLS, [1])
          MBEDTLS_ENABLED=1
          USE_MBEDTLS="yes"
-         curl_ssl_msg="enabled (mbedTLS)"
+         ssl_msg="mbedTLS"
+	 test mbedtls != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
         ], [], -lmbedx509 -lmbedcrypto)
     fi
 
@@ -2036,7 +2174,8 @@
        AC_SUBST(USE_MBEDTLS, [1])
        MBEDTLS_ENABLED=1
        USE_MBEDTLS="yes"
-       curl_ssl_msg="enabled (mbedTLS)"
+       ssl_msg="mbedTLS"
+       test mbedtls != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
        ],
        [
          CPPFLAGS=$_cppflags
@@ -2064,6 +2203,7 @@
 
   fi dnl mbedTLS not disabled
 
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
 dnl ----------------------------------------------------
@@ -2080,7 +2220,8 @@
 AC_HELP_STRING([--without-cyassl], [disable CyaSSL detection]),
   OPT_CYASSL=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_CYASSL" != xno; then
+  ssl_msg=
 
   if test X"$OPT_CYASSL" != Xno; then
 
@@ -2102,7 +2243,8 @@
          AC_SUBST(USE_CYASSL, [1])
          CYASSL_ENABLED=1
          USE_CYASSL="yes"
-         curl_ssl_msg="enabled (CyaSSL)"
+         ssl_msg="CyaSSL"
+	 test cyassl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
         ])
     fi
 
@@ -2128,7 +2270,8 @@
        AC_SUBST(USE_CYASSL, [1])
        CYASSL_ENABLED=1
        USE_CYASSL="yes"
-       curl_ssl_msg="enabled (CyaSSL)"
+       ssl_msg="CyaSSL"
+       test cyassl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
        ],
        [
          CPPFLAGS=$_cppflags
@@ -2173,7 +2316,8 @@
          AC_SUBST(USE_CYASSL, [1])
          CYASSL_ENABLED=1
          USE_CYASSL="yes"
-         curl_ssl_msg="enabled (WolfSSL)"
+         ssl_msg="WolfSSL"
+	 test cyassl != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
        ],
        [
          AC_MSG_RESULT(no)
@@ -2227,6 +2371,7 @@
 
   fi dnl CyaSSL not disabled
 
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
 dnl ----------------------------------------------------
@@ -2241,7 +2386,8 @@
 AC_HELP_STRING([--without-nss], [disable NSS detection]),
   OPT_NSS=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_NSS" != xno; then
+  ssl_msg=
 
   if test X"$OPT_NSS" != Xno; then
 
@@ -2316,7 +2462,8 @@
      AC_SUBST(USE_NSS, [1])
      USE_NSS="yes"
      NSS_ENABLED=1
-     curl_ssl_msg="enabled (NSS)"
+     ssl_msg="NSS"
+     test nss != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
      ],
      [
        LDFLAGS="$CLEANLDFLAGS"
@@ -2345,7 +2492,8 @@
 
   fi dnl NSS not disabled
 
-fi dnl curl_ssl_msg = init_ssl_msg
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
+fi
 
 OPT_AXTLS=off
 
@@ -2354,7 +2502,8 @@
 AC_HELP_STRING([--without-axtls], [disable axTLS]),
   OPT_AXTLS=$withval)
 
-if test "$curl_ssl_msg" = "$init_ssl_msg"; then
+if test -z "$ssl_backends" -o "x$OPT_AXTLS" != xno; then
+  ssl_msg=
   if test X"$OPT_AXTLS" != Xno; then
     dnl backup the pre-axtls variables
     CLEANLDFLAGS="$LDFLAGS"
@@ -2388,7 +2537,8 @@
       AC_SUBST(USE_AXTLS, [1])
       AXTLS_ENABLED=1
       USE_AXTLS="yes"
-      curl_ssl_msg="enabled (axTLS)"
+      ssl_msg="axTLS"
+      test axtls != "$DEFAULT_SSL_BACKEND" || VALID_DEFAULT_SSL_BACKEND=yes
 
       if test "x$cross_compiling" != "xyes"; then
         LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$LIB_AXTLS"
@@ -2401,15 +2551,46 @@
       LIBS="$CLEANLIBS"
     ])
   fi
+  test -z "$ssl_msg" || ssl_backends="${ssl_backends:+$ssl_backends, }$ssl_msg"
 fi
 
-if test "x$OPENSSL_ENABLED$GNUTLS_ENABLED$NSS_ENABLED$POLARSSL_ENABLED$MBEDTLS_ENABLED$AXTLS_ENABLED$CYASSL_ENABLED$WINSSL_ENABLED$DARWINSSL_ENABLED" = "x"; then
+case "x$OPENSSL_ENABLED$GNUTLS_ENABLED$NSS_ENABLED$POLARSSL_ENABLED$MBEDTLS_ENABLED$AXTLS_ENABLED$CYASSL_ENABLED$WINSSL_ENABLED$DARWINSSL_ENABLED" in
+x)
   AC_MSG_WARN([SSL disabled, you will not be able to use HTTPS, FTPS, NTLM and more.])
   AC_MSG_WARN([Use --with-ssl, --with-gnutls, --with-polarssl, --with-cyassl, --with-nss, --with-axtls, --with-winssl, or --with-darwinssl to address this.])
-else
-  # SSL is enabled, genericly
+  ;;
+x1)
+  # one SSL backend is enabled
   AC_SUBST(SSL_ENABLED)
   SSL_ENABLED="1"
+  AC_MSG_NOTICE([built with one SSL backend])
+  ;;
+*)
+  # more than one SSL backend is enabled
+  AC_SUBST(SSL_ENABLED)
+  SSL_ENABLED="1"
+  AC_SUBST(CURL_WITH_MULTI_SSL)
+  CURL_WITH_MULTI_SSL="1"
+  AC_DEFINE(CURL_WITH_MULTI_SSL, 1, [built with multiple SSL backends])
+  AC_MSG_NOTICE([built with multiple SSL backends])
+  ;;
+esac
+
+if test -n "$ssl_backends"; then
+  curl_ssl_msg="enabled ($ssl_backends)"
+fi
+
+if test no = "$VALID_DEFAULT_SSL_BACKEND"
+then
+  if test -n "$SSL_ENABLED"
+  then
+    AC_MSG_ERROR([Default SSL backend $DEFAULT_SSL_BACKEND not enabled!])
+  else
+    AC_MSG_ERROR([Default SSL backend requires SSL!])
+  fi
+elif test yes = "$VALID_DEFAULT_SSL_BACKEND"
+then
+  AC_DEFINE_UNQUOTED([CURL_DEFAULT_SSL_BACKEND], ["$DEFAULT_SSL_BACKEND"], [Default SSL backend])
 fi
 
 dnl **********************************************************************
@@ -2710,7 +2891,9 @@
         AC_MSG_WARN([You need an ld version supporting the --version-script option])
     else
         AC_MSG_RESULT(yes)
-        if test "x$OPENSSL_ENABLED" = "x1"; then
+        if test "x$CURL_WITH_MULTI_SSL" = "x1"; then
+          versioned_symbols_flavour="MULTISSL_"
+        elif test "x$OPENSSL_ENABLED" = "x1"; then
           versioned_symbols_flavour="OPENSSL_"
         elif test "x$GNUTLS_ENABLED" = "x1"; then
           versioned_symbols_flavour="GNUTLS_"
@@ -3092,6 +3275,7 @@
         net/if.h \
         netinet/in.h \
         sys/un.h \
+        linux/tcp.h \
         netinet/tcp.h \
         netdb.h \
         sys/sockio.h \
@@ -3158,18 +3342,15 @@
 AC_CHECK_SIZEOF(long)
 AC_CHECK_SIZEOF(int)
 AC_CHECK_SIZEOF(short)
-CURL_CONFIGURE_LONG
 AC_CHECK_SIZEOF(time_t)
 AC_CHECK_SIZEOF(off_t)
 
-soname_bump=no
-if test x"$curl_cv_native_windows" != "xyes" &&
-   test $ac_cv_sizeof_off_t -ne $curl_sizeof_curl_off_t; then
-  AC_MSG_WARN([This libcurl built is probably not ABI compatible with previous])
-  AC_MSG_WARN([builds! You MUST read lib/README.curl_off_t to figure it out.])
-  soname_bump=yes
-fi
-
+o=$CPPFLAGS
+CPPFLAGS="-I$srcdir/include $CPPFLAGS"
+AC_CHECK_SIZEOF(curl_off_t, unused , [
+#include <curl/system.h>
+])
+CPPFLAGS=$o
 
 AC_CHECK_TYPE(long long,
    [AC_DEFINE(HAVE_LONGLONG, 1,
@@ -3294,6 +3475,7 @@
   getrlimit \
   gettimeofday \
   if_nametoindex \
+  mach_absolute_time \
   pipe \
   setlocale \
   setmode \
@@ -3648,26 +3830,6 @@
 dnl
 CURL_CONFIGURE_SYMBOL_HIDING
 
-dnl ************************************************************
-dnl enforce SONAME bump
-dnl
-
-AC_MSG_CHECKING([whether to enforce SONAME bump])
-AC_ARG_ENABLE(soname-bump,
-AC_HELP_STRING([--enable-soname-bump],[Enable enforced SONAME bump])
-AC_HELP_STRING([--disable-soname-bump],[Disable enforced SONAME bump]),
-[ case "$enableval" in
-  yes)   AC_MSG_RESULT(yes)
-         soname_bump=yes
-         ;;
-  *)
-         AC_MSG_RESULT(no)
-         ;;
-  esac ],
-        AC_MSG_RESULT($soname_bump)
-)
-AM_CONDITIONAL(SONAME_BUMP, test x$soname_bump = xyes)
-
 dnl
 dnl All the library dependencies put into $LIB apply to libcurl only.
 dnl
@@ -3714,6 +3876,9 @@
 if test "x$HAVE_LIBZ" = "x1"; then
   SUPPORT_FEATURES="$SUPPORT_FEATURES libz"
 fi
+if test "x$HAVE_BROTLI" = "x1"; then
+  SUPPORT_FEATURES="$SUPPORT_FEATURES brotli"
+fi
 if test "x$USE_ARES" = "x1" -o "x$USE_THREADS_POSIX" = "x1" \
                             -o "x$USE_THREADS_WIN32" = "x1"; then
   SUPPORT_FEATURES="$SUPPORT_FEATURES AsynchDNS"
@@ -3764,6 +3929,10 @@
   SUPPORT_FEATURES="$SUPPORT_FEATURES HTTP2"
 fi
 
+if test "x$CURL_WITH_MULTI_SSL" = "x1"; then
+  SUPPORT_FEATURES="$SUPPORT_FEATURES MultiSSL"
+fi
+
 if test "x$OPENSSL_ENABLED" = "x1" -o "x$GNUTLS_ENABLED" = "x1" \
     -o "x$NSS_ENABLED" = "x1"; then
   SUPPORT_FEATURES="$SUPPORT_FEATURES HTTPS-proxy"
@@ -3895,7 +4064,6 @@
            tests/server/Makefile \
            tests/libtest/Makefile \
            tests/unit/Makefile \
-           tests/fuzz/Makefile \
            packages/Makefile \
            packages/Win32/Makefile \
            packages/Win32/cygwin/Makefile \
@@ -3928,6 +4096,7 @@
   SSL support:      ${curl_ssl_msg}
   SSH support:      ${curl_ssh_msg}
   zlib support:     ${curl_zlib_msg}
+  brotli support:   ${curl_brotli_msg}
   GSS-API support:  ${curl_gss_msg}
   TLS-SRP support:  ${curl_tls_srp_msg}
   resolver:         ${curl_res_msg}
@@ -3951,14 +4120,3 @@
   HTTP2 support:    ${curl_h2_msg}
   Protocols:        ${SUPPORT_PROTOCOLS}
 ])
-
-if test "x$soname_bump" = "xyes"; then
-
-cat <<EOM
-  SONAME bump:     yes - WARNING: this library will be built with the SONAME
-                   number bumped due to (a detected) ABI breakage.
-                   See lib/README.curl_off_t for details on this.
-EOM
-
-fi
-