-Wformat: fix nonsensical "wide character" message (PR c/84258)

gcc/c-family/ChangeLog:
	PR c/84258
	* c-format.c (struct format_check_results): Add field
	"number_non_char".
	(check_format_info): Initialize it, and warn if encountered.
	(check_format_arg): Distinguish between wide char and
	everything else when detecting arrays of non-char.

gcc/testsuite/ChangeLog:
	PR c/84258
	* c-c++-common/Wformat-pr84258.c: New test.

From-SVN: r259807