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>

cache.h

@@ -961,7 +961,9 @@ extern void *alloc_object_node(void);
 extern void alloc_report(void);
 
 /* trace.c */
+__attribute__((format (printf, 1, 2)))
 extern void trace_printf(const char *format, ...);
+__attribute__((format (printf, 2, 3)))
 extern void trace_argv_printf(const char **argv, const char *format, ...);
 
 /* convert.c */