configure: Always add pre-installed header directories to search path

configure script was adding the target directory flags, including the
'-B' flags for the executable prefix and the '-isystem' flags for the
pre-installed header directories, to the target flags only for
non-Canadian builds under the premise that the host binaries under the
executable prefix will not be able to execute on the build system for
Canadian builds.

While that is true for the '-B' flags specifying the executable prefix,
the '-isystem' flags specifying the pre-installed header directories are
not affected by this and do not need special handling.

This patch updates the configure script to always add the 'include' and
'sys-include' pre-installed header directories to the target search
path, in order to ensure that the availability of the pre-installed
header directories in the search path is consistent across non-Canadian
and Canadian builds.

When '--with-headers' flag is specified, this effectively ensures that
the libc headers, that are copied from the specified header directory to
the sys-include directory, are used by libstdc++.

ChangeLog:

    * configure.ac: Always add sys-include to search path.
    * configure: Regenerate.

Signed-off-by: Stephanos Ioannidis <[email protected]>

configure

@@ -10251,13 +10251,17 @@ if test x"${build}" = x"${host}" ; then
   LDFLAGS_FOR_BUILD=${LDFLAGS_FOR_BUILD-${LDFLAGS}}
 fi
 
-# On Canadian crosses, we'll be searching the right directories for
-# the previously-installed cross compiler, so don't bother to add
-# flags for directories within the install tree of the compiler
-# being built; programs in there won't even run.
-if test "${build}" = "${host}" && test -d ${srcdir}/gcc; then
+if test -d ${srcdir}/gcc; then
+  # On Canadian crosses, we'll be searching the right directories for the
+  # previously-installed cross compiler, so don't bother to add flags for
+  # executable directories within the install tree of the compiler being built;
+  # programs in there won't even run.
+  if test "${build}" = "${host}"; then
+    FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' -B$(build_tooldir)/bin/ -B$(build_tooldir)/lib/'
+  fi
+
   # Search for pre-installed headers if nothing else fits.
-  FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' -B$(build_tooldir)/bin/ -B$(build_tooldir)/lib/ -isystem $(build_tooldir)/include -isystem $(build_tooldir)/sys-include'
+  FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' -isystem $(build_tooldir)/include -isystem $(build_tooldir)/sys-include'
 fi
 
 if test "x${use_gnu_ld}" = x &&

configure.ac

@@ -3432,13 +3432,17 @@ if test x"${build}" = x"${host}" ; then
   LDFLAGS_FOR_BUILD=${LDFLAGS_FOR_BUILD-${LDFLAGS}}
 fi
 
-# On Canadian crosses, we'll be searching the right directories for
-# the previously-installed cross compiler, so don't bother to add
-# flags for directories within the install tree of the compiler
-# being built; programs in there won't even run.
-if test "${build}" = "${host}" && test -d ${srcdir}/gcc; then
+if test -d ${srcdir}/gcc; then
+  # On Canadian crosses, we'll be searching the right directories for the
+  # previously-installed cross compiler, so don't bother to add flags for
+  # executable directories within the install tree of the compiler being built;
+  # programs in there won't even run.
+  if test "${build}" = "${host}"; then
+    FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' -B$(build_tooldir)/bin/ -B$(build_tooldir)/lib/'
+  fi
+
   # Search for pre-installed headers if nothing else fits.
-  FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' -B$(build_tooldir)/bin/ -B$(build_tooldir)/lib/ -isystem $(build_tooldir)/include -isystem $(build_tooldir)/sys-include'
+  FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' -isystem $(build_tooldir)/include -isystem $(build_tooldir)/sys-include'
 fi
 
 if test "x${use_gnu_ld}" = x &&