c: reorganize recursive type checking

c: reorganize recursive type checking

Reorganize recursive type checking to use a structure to
store information collected during the recursion and
returned to the caller (warning_needed, enum_and_init_p,
different_types_p).

gcc/c:
	* c-typeck.cc (struct comptypes_data): Add structure.
	(tagged_types_tu_compatible_p,
	function_types_compatible_p, type_lists_compatible_p,
	comptypes_internal): Add structure to interface, change
	return type to bool, and adapt calls.
	(comptarget_types): Change return type too bool.
	(comptypes, comptypes_check_enum_int,
	comptypes_check_different_types): Adapt calls.