Make keyed_classes a vector.

	* cp-tree.h (CPTI_KEYED_CLASSES, keyed_classes): Delete.
	(keyed_classes): Declare as vector.
	* decl.c (keyed_classes): Define.
	(cxx_init_decl_processing): Allocate it.
	(record_key_method_defined): Use vec_safe_push.
	* class.c (finish_struct_1): Likewise.
	* pt.c (instantiate_class_template_1): Likewise.
	* decl2.c (c_parse_final_cleanups): Reverse iterate keyed_classes.

From-SVN: r249263