c-family: add support for per-location warning groups.

c-family: add support for per-location warning groups.

gcc/c-family/ChangeLog:

	* c-common.c (c_wrap_maybe_const): Remove TREE_NO_WARNING.
	(c_common_truthvalue_conversion): Replace direct uses of
	TREE_NO_WARNING with warning_suppressed_p, suppress_warning, and
	copy_no_warning.
	(check_function_arguments_recurse): Same.
	* c-gimplify.c (c_gimplify_expr): Same.
	* c-warn.c (overflow_warning): Same.
	(warn_logical_operator): Same.
	(warn_if_unused_value): Same.
	(do_warn_unused_parameter): Same.