Check the format of more printf-type functions

We already have these checks in many printf-type functions that have
prototypes which are in header files.  Add these same checks to some
more prototypes in header functions and to static functions in .c
files.

cc: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Tarmigan Casebolt <tarmigan+git@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-upload-archive.c

@@ -67,6 +67,7 @@ static int run_upload_archive(int argc, const char **argv, const char *prefix)
 	return write_archive(sent_argc, sent_argv, prefix, 0);
 }
 
+__attribute__((format (printf, 1, 2)))
 static void error_clnt(const char *fmt, ...)
 {
 	char buf[1024];