GCC: Pass --plugin to AR and RANLIB

Detect GCC LTO plugin.  Pass --plugin to AR and RANLIB to support LTO
build.

	* Makefile.tpl (AR): Add @AR_PLUGIN_OPTION@
	(RANLIB): Add @RANLIB_PLUGIN_OPTION@.
	* configure.ac: Include config/gcc-plugin.m4.
	AC_SUBST AR_PLUGIN_OPTION and RANLIB_PLUGIN_OPTION.
	* libtool.m4 (_LT_CMD_OLD_ARCHIVE): Pass --plugin to AR and
	RANLIB if possible.
	* Makefile.in: Regenerated.
	* configure: Likewise.

config/

	* gcc-plugin.m4 (GCC_PLUGIN_OPTION): New.

libiberty/

	* Makefile.in (AR): Add @AR_PLUGIN_OPTION@
	(RANLIB): Add @RANLIB_PLUGIN_OPTION@.
	(configure_deps): Depend on ../config/gcc-plugin.m4.
	* aclocal.m4: Include ../config/gcc-plugin.m4.
	* configure.ac: AC_SUBST AR_PLUGIN_OPTION and
	RANLIB_PLUGIN_OPTION.
	* configure: Regenerated.

zlib/

	* configure: Regenerated.