Remove ${srcroot} from cfghdrs_in, cfgoutputs_in and cfghdrs_tup in configure

On Windows, srcroot may start with "drive:", which confuses autoconf's
AC_CONFIG_* macros. The macros works equally well without ${srcroot},
provided some adjustment to Makefile.in.
diff --git a/configure.ac b/configure.ac
index 645bd46..bc3464f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -534,15 +534,15 @@
 je_="je_"
 AC_SUBST([je_])
 
-cfgoutputs_in="${srcroot}Makefile.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}doc/html.xsl.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}doc/manpages.xsl.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}doc/jemalloc.xml.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}include/jemalloc/jemalloc_macros.h.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}include/jemalloc/jemalloc_protos.h.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}include/jemalloc/internal/jemalloc_internal.h.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}test/test.sh.in"
-cfgoutputs_in="${cfgoutputs_in} ${srcroot}test/include/test/jemalloc_test.h.in"
+cfgoutputs_in="Makefile.in"
+cfgoutputs_in="${cfgoutputs_in} doc/html.xsl.in"
+cfgoutputs_in="${cfgoutputs_in} doc/manpages.xsl.in"
+cfgoutputs_in="${cfgoutputs_in} doc/jemalloc.xml.in"
+cfgoutputs_in="${cfgoutputs_in} include/jemalloc/jemalloc_macros.h.in"
+cfgoutputs_in="${cfgoutputs_in} include/jemalloc/jemalloc_protos.h.in"
+cfgoutputs_in="${cfgoutputs_in} include/jemalloc/internal/jemalloc_internal.h.in"
+cfgoutputs_in="${cfgoutputs_in} test/test.sh.in"
+cfgoutputs_in="${cfgoutputs_in} test/include/test/jemalloc_test.h.in"
 
 cfgoutputs_out="Makefile"
 cfgoutputs_out="${cfgoutputs_out} doc/html.xsl"
@@ -564,18 +564,18 @@
 cfgoutputs_tup="${cfgoutputs_tup} test/test.sh:test/test.sh.in"
 cfgoutputs_tup="${cfgoutputs_tup} test/include/test/jemalloc_test.h:test/include/test/jemalloc_test.h.in"
 
-cfghdrs_in="${srcroot}include/jemalloc/jemalloc_defs.h.in"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/jemalloc_internal_defs.h.in"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/private_namespace.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/private_unnamespace.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/private_symbols.txt"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/public_namespace.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/public_unnamespace.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/internal/size_classes.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/jemalloc_rename.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/jemalloc_mangle.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}include/jemalloc/jemalloc.sh"
-cfghdrs_in="${cfghdrs_in} ${srcroot}test/include/test/jemalloc_test_defs.h.in"
+cfghdrs_in="include/jemalloc/jemalloc_defs.h.in"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/jemalloc_internal_defs.h.in"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/private_namespace.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/private_unnamespace.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/private_symbols.txt"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/public_namespace.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/public_unnamespace.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/internal/size_classes.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/jemalloc_rename.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/jemalloc_mangle.sh"
+cfghdrs_in="${cfghdrs_in} include/jemalloc/jemalloc.sh"
+cfghdrs_in="${cfghdrs_in} test/include/test/jemalloc_test_defs.h.in"
 
 cfghdrs_out="include/jemalloc/jemalloc_defs.h"
 cfghdrs_out="${cfghdrs_out} include/jemalloc/jemalloc${install_suffix}.h"
@@ -593,8 +593,8 @@
 cfghdrs_out="${cfghdrs_out} test/include/test/jemalloc_test_defs.h"
 
 cfghdrs_tup="include/jemalloc/jemalloc_defs.h:include/jemalloc/jemalloc_defs.h.in"
-cfghdrs_tup="${cfghdrs_tup} include/jemalloc/internal/jemalloc_internal_defs.h:${srcroot}include/jemalloc/internal/jemalloc_internal_defs.h.in"
-cfghdrs_tup="${cfghdrs_tup} test/include/test/jemalloc_test_defs.h:${srcroot}test/include/test/jemalloc_test_defs.h.in"
+cfghdrs_tup="${cfghdrs_tup} include/jemalloc/internal/jemalloc_internal_defs.h:include/jemalloc/internal/jemalloc_internal_defs.h.in"
+cfghdrs_tup="${cfghdrs_tup} test/include/test/jemalloc_test_defs.h:test/include/test/jemalloc_test_defs.h.in"
 
 dnl Silence irrelevant compiler warnings by default.
 AC_ARG_ENABLE([cc-silence],