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-update-index.c

@@ -27,6 +27,7 @@ static int mark_valid_only;
 #define MARK_VALID 1
 #define UNMARK_VALID 2
 
+__attribute__((format (printf, 1, 2)))
 static void report(const char *fmt, ...)
 {
 	va_list vp;