Move ipa-refs from ggc to heap.

Move ipa-refs from ggc to heap.

gcc/ChangeLog:

	* ipa-ref.h (enum ipa_ref_use): Remove GTY marker.
	(struct ipa_ref): Remove GTY marker; reorder for better packing.
	(struct ipa_ref_list): Remove GTY marker; turn references
	nad referring to va_heap, vl_ptr vectors; update accesors.
	* cgraph.h (symtab_node::iterate_reference): Update.
	* ipa-ref.c (ipa_ref::remove_reference): Update.
	* symtab.c (symtab_node::create_reference): Update.
	(symtab_node::remove_all_references): Update.
	(symtab_node::resolve_alias): Update.

gcc/cp/ChangeLog:

	* tree.c (cp_fix_function_decl_p): Do not access ipa_ref_list dirrectly.