Handle fnspec in local ipa-modref

Handle fnspec in local ipa-modref

	* ipa-modref.c (modref_summary::dump): Dump writes_errno.
	(parm_map_for_arg): Break out from ...
	(merge_call_side_effects): ... here.
	(get_access_for_fnspec): New function.
	(process_fnspec): New function.
	(analyze_call): Use it.
	(analyze_stmt): Update.
	(analyze_function): Initialize writes_errno.
	(modref_summaries::duplicate): Duplicate writes_errno.
	* ipa-modref.h (struct modref_summary): Add writes_errno.
	* tree-ssa-alias.c (call_may_clobber_ref_p_1): Check errno.