Add `--with-toolexeclibdir=' configuration option

Provide means, in the form of a `--with-toolexeclibdir=' configuration
option, to override the default installation directory for target
libraries, otherwise known as $toolexeclibdir.  This is so that it is
possible to get newly-built libraries, particularly the shared ones,
installed in a common place, so that they can be readily used by the
target system as their host libraries, possibly over NFS, without a need
to manually copy them over from the currently hardcoded location they
would otherwise be installed in.

In the presence of the `--enable-version-specific-runtime-libs' option
and for configurations building native GCC the option is ignored.

	config/
	* toolexeclibdir.m4: New file.

	gcc/
	* doc/install.texi (Cross-Compiler-Specific Options): Document
	`--with-toolexeclibdir' option.

	libada/
	* Makefile.in (configure_deps): Add `toolexeclibdir.m4'.
	* configure.ac: Handle `--with-toolexeclibdir='.
	* configure: Regenerate.

	libatomic/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* testsuite/Makefile.in: Regenerate.

	libffi/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* include/Makefile.in: Regenerate.
	* man/Makefile.in: Regenerate.
	* testsuite/Makefile.in: Regenerate.

	libgcc/
	* Makefile.in (configure_deps): Add `toolexeclibdir.m4'.
	* configure.ac: Handle `--with-toolexeclibdir='.
	* configure: Regenerate.

	libgfortran/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	libgomp/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* testsuite/Makefile.in: Regenerate.

	libhsail-rt/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	libitm/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* testsuite/Makefile.in: Regenerate.

	libobjc/
	* Makefile.in (aclocal_deps): Add `toolexeclibdir.m4'.
	* aclocal.m4: Include `toolexeclibdir.m4'.
	* configure.ac: Handle `--with-toolexeclibdir='.
	* configure: Regenerate.

	liboffloadmic/
	* plugin/configure.ac: Handle `--with-toolexeclibdir='.
	* plugin/Makefile.in: Regenerate.
	* plugin/aclocal.m4: Regenerate.
	* plugin/configure: Regenerate.
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	libphobos/
	* m4/druntime.m4: Handle `--with-toolexeclibdir='.
	* m4/Makefile.in: Regenerate.
	* libdruntime/Makefile.in: Regenerate.
	* src/Makefile.in: Regenerate.
	* testsuite/Makefile.in: Regenerate.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	libquadmath/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	libsanitizer/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* asan/Makefile.in: Regenerate.
	* interception/Makefile.in: Regenerate.
	* libbacktrace/Makefile.in: Regenerate.
	* lsan/Makefile.in: Regenerate.
	* sanitizer_common/Makefile.in: Regenerate.
	* tsan/Makefile.in: Regenerate.
	* ubsan/Makefile.in: Regenerate.

	libssp/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.

	libstdc++-v3/
	* acinclude.m4: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* doc/Makefile.in: Regenerate.
	* include/Makefile.in: Regenerate.
	* libsupc++/Makefile.in: Regenerate.
	* po/Makefile.in: Regenerate.
	* python/Makefile.in: Regenerate.
	* src/Makefile.in: Regenerate.
	* src/c++11/Makefile.in: Regenerate.
	* src/c++17/Makefile.in: Regenerate.
	* src/c++98/Makefile.in: Regenerate.
	* src/filesystem/Makefile.in: Regenerate.
	* testsuite/Makefile.in: Regenerate.

	libvtv/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.
	* testsuite/Makefile.in: Regenerate.

	zlib/
	* configure.ac: Handle `--with-toolexeclibdir='.
	* Makefile.in: Regenerate.
	* aclocal.m4: Regenerate.
	* configure: Regenerate.