Add very basic IPA part of modref-kill analysis

Add very basic IPA part of modref-kill analysis

gcc/ChangeLog:

2021-11-17  Jan Hubicka  <hubicka@ucw.cz>

	* ipa-modref-tree.c: Include cgraph.h and tree-streamer.h.
	(modref_access_node::stream_out): New member function.
	(modref_access_node::stream_in): New member function.
	* ipa-modref-tree.h (modref_access_node::stream_out,
	modref_access_node::stream_in): Declare.
	* ipa-modref.c (modref_summary_lto::useful_p): Free useless kills.
	(modref_summary_lto::dump): Dump kills.
	(analyze_store): Record kills for LTO
	(analyze_stmt): Likewise.
	(modref_summaries_lto::duplicate): Duplicate kills.
	(write_modref_records): Use new stream_out member function.
	(read_modref_records): Likewise.
	(modref_write): Stream out kills.
	(read_section): Stream in kills
	(remap_kills): New function.
	(update_signature): Use it.