Use GCC_FMT_ATTR (format checking)

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/disas.c b/disas.c
index 79a98de..afe331f 100644
--- a/disas.c
+++ b/disas.c
@@ -349,7 +349,8 @@
     return 0;
 }
 
-static int monitor_fprintf(FILE *stream, const char *fmt, ...)
+static int GCC_FMT_ATTR(2, 3)
+monitor_fprintf(FILE *stream, const char *fmt, ...)
 {
     va_list ap;
     va_start(ap, fmt);