Partially revert "automake: allow only shared builds"

Evidently at least static OSMesa is still used as shared one
causes substantial increase in the load time for some programs
that use it (from seconds up-to ~30min).

Rather than forcing everyone to use shared mesa, revert commit
a6efbac9fb502c4f0166e7a0680b6828e1f6926c and default to shared
build when both shared and static are disabled.

v2: Whitespace cleanup, drop silly comment.

Reported-by: Burlen Loring <burlen.loring@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
diff --git a/configure.ac b/configure.ac
index ecf66a3..cad4b05 100644
--- a/configure.ac
+++ b/configure.ac
@@ -284,15 +284,18 @@
 dnl explicitly requested. If both disabled, set to static since shared
 dnl was explicitly requested.
 case "x$enable_static$enable_shared" in
-xnoyes )
+xyesyes)
+    AC_MSG_WARN([Cannot build static and shared libraries, disabling shared])
+    enable_shared=no
     ;;
-* )
-    AC_MSG_WARN([Messa build supports only shared libraries, enabling shared])
+xnono)
+    AC_MSG_WARN([Cannot disable both static and shared libraries, enabling shared])
     enable_shared=yes
-    enable_static=no
     ;;
 esac
 
+AM_CONDITIONAL(BUILD_SHARED, test "x$enable_shared" = xyes)
+
 dnl
 dnl other compiler options
 dnl
@@ -782,6 +785,10 @@
                   have_libudev=yes, have_libudev=no)
 
 if test "x$enable_dri" = xyes; then
+    if test "$enable_static" = yes; then
+        AC_MSG_ERROR([Cannot use static libraries for DRI drivers])
+    fi
+
     # not a hard requirement as swrast does not depend on it
     if test "x$have_libdrm" = xyes; then
         DRI_PC_REQ_PRIV="libdrm >= $LIBDRM_REQUIRED"
@@ -1110,7 +1117,12 @@
 esac
 
 if test "x$enable_osmesa" = xyes -o "x$enable_gallium_osmesa" = xyes; then
-    OSMESA_LIB_DEPS="-lm $PTHREAD_LIBS $SELINUX_LIBS $DLOPEN_LIBS"
+    # only link libraries with osmesa if shared
+    if test "$enable_static" = no; then
+        OSMESA_LIB_DEPS="-lm $PTHREAD_LIBS $SELINUX_LIBS $DLOPEN_LIBS"
+    else
+        OSMESA_LIB_DEPS=""
+    fi
     OSMESA_MESA_DEPS=""
     OSMESA_PC_LIB_PRIV="-lm $PTHREAD_LIBS $SELINUX_LIBS $DLOPEN_LIBS"
 fi
@@ -1159,8 +1171,11 @@
 
     AC_CHECK_FUNC(mincore, [DEFINES="$DEFINES -DHAVE_MINCORE"])
 
-    if test "x$enable_dri" = xyes; then
-        HAVE_EGL_DRIVER_DRI2=1
+    if test "$enable_static" != yes; then
+        if test "x$enable_dri" = xyes; then
+	    HAVE_EGL_DRIVER_DRI2=1
+	fi
+
     fi
 fi
 AM_CONDITIONAL(HAVE_EGL, test "x$enable_egl" = xyes)