Partial fix PR c++/12850
	* cgraphunit.c (cgraph_finalize_function): Always ggc_collect when
	at zero nest level.

	* decl2.c (mark_used): Do not proactively instantiate templates
	when compiling in unit-at-a-time or not optimizing.
	* optimize.c (maybe_clone_body): Do not increase function depth.

From-SVN: r75823