Non-host system configuration for linker plugins.

	* configure.ac (--enable-linker-plugin-configure-flags)
	(--enable-linker-plugin-flags): New flags.
	(configdirs): Conditionally add libiberty-linker-plugin.
	* configure: Regenerate.
	* Makefile.def (host_modules): Add libiberty-linker-plugin.
	(host_modules) <lto-plugin>: Pay attention to
	@extra_linker_plugin_flags@ and
	@extra_linker_plugin_configure_flags@.
	(all-lto-plugin): Also depend on all-libiberty-linker-plugin.
	* Makefile.in: Regenerate.
	gcc/
	* doc/install.texi (--enable-linker-plugin-configure-flags)
	(--enable-linker-plugin-flags): Document new flags.

From-SVN: r211644