*.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>

mailmap.c

@@ -8,6 +8,7 @@
 #define debug_mm(...) fprintf(stderr, __VA_ARGS__)
 #define debug_str(X) ((X) ? (X) : "(none)")
 #else
+__attribute__((format (printf, 1, 2)))
 static inline void debug_mm(const char *format, ...) {}
 static inline const char *debug_str(const char *s) { return s; }
 #endif