invoke.texi (ffat-lto-objects): Document.

	* doc/invoke.texi (ffat-lto-objects): Document.
	* toplev.c (compile_file): Do not output assembly when doing slim lto;
	Output __gnu_slim_lto when doing slim lto.
	* cgraphunit.c (ipa_passes): Do only analysis when producing slim lto.
	(cgraph_optimize): Return early when doing slim lto.
	* opts.c (finish_options): Complain about lack of linker plugin
	when doing slim lto.
	* common.opt (ffat-lto-objects): New.

Co-Authored-By: Jan Hubicka <jh@suse.cz>

From-SVN: r179271