*.c static functions: add missing __attribute__((format))

Add missing __attribute__((format)) function attributes to various
"static" functions that take printf arguments.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gettext.c

@@ -66,6 +66,7 @@ const char *get_preferred_languages(void)
 }
 
 #ifndef NO_GETTEXT
+__attribute__((format (printf, 1, 2)))
 static int test_vsnprintf(const char *fmt, ...)
 {
 	char buf[26];