PR target/88638 - FAIL: fsf-nsstring-format-1.s on darwin

PR target/88638 - FAIL: fsf-nsstring-format-1.s on darwin

gcc/c-family/ChangeLog:

	PR target/88638
	* c-attribs.c (positional_argument): Call valid_format_string_type_p
	and issue errors if it fails.
	* c-common.h (valid_format_string_type_p): Declare.
	* c-format.c (valid_stringptr_type_p): Rename...
	(valid_format_string_type_p): ...to this and make extern.
	(handle_format_arg_attribute): Adjust to new name.
	(check_format_string): Same.

gcc/testsuite/ChangeLog:

	PR target/88638
	* gcc.dg/format/attr-8.c: New test.
	* gcc.dg/darwin-cfstring-format-1.c: Adjust diagnostics.
	* gcc.dg/format/attr-3.c: Same.
	* obj-c++.dg/fsf-nsstring-format-1.mm: Same.
	* objc.dg/fsf-nsstring-format-1.m: Same.

gcc/ChangeLog:

	PR target/88638
	* doc/extend.texi (Darwin Format Checks): Clarify.

From-SVN: r267922