MT#57281 Mark medredis_command() with printf attribute

Add macros to handle attributes transparently and make their usage
easier.

Change-Id: I0e1025bf827736e5a09e477d8fb03dee8e33460c

mediator.h

@@ -13,6 +13,20 @@
 #include <inttypes.h>
 #include <json.h>
 
+/* Compiler support. */
+
+/* Supported since gcc 5.1.0 and clang 2.9.0. */
+#ifndef __has_attribute
+#define __has_attribute(x)	0
+#endif
+
+#if __has_attribute(__format__)
+#define MEDIATOR_ATTR_FORMAT(type, fmt, args) __attribute__((__format__(type, fmt, args)))
+#define MEDIATOR_ATTR_PRINTF(fmt, args) MEDIATOR_ATTR_FORMAT(__printf__, fmt, args)
+#else
+#define MEDIATOR_ATTR_FORMAT(type, fmt, args)
+#define MEDIATOR_ATTR_PRINTF(fmt, args)
+#endif
 
 #define MEDIATOR_DEFAULT_INTERVAL 10
 

medredis.c

@@ -136,6 +136,7 @@ err:
 }
 
 /**********************************************************************/
+MEDIATOR_ATTR_PRINTF(1, 2)
 static redisReply *medredis_command(const char* cmd, ...) {
     va_list args;