Make canonical_va_list_type more strict

Make canonical_va_list_type more strict

2016-09-10  Tom de Vries  <tom@codesourcery.com>

	PR C/71602
	* builtins.c (std_canonical_va_list_type): Strictly return non-null for
	va_list type only.
	* config/i386/i386.c (ix86_canonical_va_list_type): Same.
	* gimplify.c (gimplify_va_arg_expr): Handle &va_list.

	* c-common.c (build_va_arg): Handle more strict
	targetm.canonical_va_list_type.  Replace first argument type error with
	assert.

	* c-c++-common/va-arg-va-list-type.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@240072 138bc75d-0d04-0410-961f-82ee72b054a4