re PR driver/46944 (gcc should accept -fuse-linker-plugin only if linker handles -plugin)

	PR lto/46944
	* configure.ac (gcc_cv_gld_major_version, gcc_cv_gld_minor):
	Handle in-tree gold.
	(ld_vers): Extract binutils version for gold.
	(gcc_cv_ld_hidden): Handle gold here.
	(gcc_cv_lto_plugin): Determine level of linker plugin support.
	* configure: Regenerate.
	* config.in: Regenerate.
	* gcc.c: Only use LTO plugin if HAVE_LTO_PLUGIN > 0, reject
	-fuse-linker-plugin otherwise.
	(LINK_PLUGIN_SPEC): Define.  Extract from LINK_COMMAND_SPEC.
	(LINK_COMMAND_SPEC): Use it.
	(main): Only look for LTOPLUGINSONAME if HAVE_LTO_PLUGIN > 0.

From-SVN: r171039