Static chain support in ipa-modref

Static chain support in ipa-modref

Teach ipa-modref about the static chain that is, like
retslot, a hiden argument.  The patch is pretty much symemtric to what
was done for retslot handling and I verified it does the intended job
for Ada LTO bootstrap.

gcc/ChangeLog:

	* gimple.c (gimple_call_static_chain_flags): New function.
	* gimple.h (gimple_call_static_chain_flags): Declare
	* ipa-modref.c (modref_summary::modref_summary): Initialize
	static_chain_flags.
	(modref_summary_lto::modref_summary_lto): Likewise.
	(modref_summary::useful_p): Test static_chain_flags.
	(modref_summary_lto::useful_p): Likewise.
	(struct modref_summary_lto): Add static_chain_flags.
	(modref_summary::dump): Dump static_chain_flags.
	(modref_summary_lto::dump): Likewise.
	(struct escape_point): Add static_cahin_arg.
	(analyze_ssa_name_flags): Use gimple_call_static_chain_flags.
	(analyze_parms): Handle static chains.
	(modref_summaries::duplicate): Duplicate static_chain_flags.
	(modref_summaries_lto::duplicate): Likewise.
	(modref_write): Stream static_chain_flags.
	(read_section): Likewise.
	(modref_merge_call_site_flags): Handle static_chain_flags.
	* ipa-modref.h (struct modref_summary): Add static_chain_flags.
	* tree-ssa-structalias.c (handle_rhs_call): Use
	gimple_static_chain_flags.

gcc/testsuite/ChangeLog:

	* gcc.dg/ipa/modref-3.c: New test.