Add format checks for printf-style functions

Added format checks to functions that expect printf style arguments and
fixed any broken calls to these functions.

include/maxscale/cdefs.h

@@ -79,6 +79,17 @@
  */
 #define MXS_MAX(a,b) ((a)>(b) ? (a) : (b))
 
+/**
+ * Define function attributes
+ *
+ * The function attributes are compiler specific.
+ */
+#ifdef __GNUC__
+#define mxs_attribute(a) __attribute__(a)
+#else
+#define mxs_attribute(a)
+#endif
+
 /**
  * COMMON INCLUDE FILES
  */

include/maxscale/log_manager.h

@@ -119,7 +119,7 @@ static inline bool mxs_log_priority_is_enabled(int priority)
 int mxs_log_message(int priority,
                     const char* modname,
                     const char* file, int line, const char* function,
-                    const char* format, ...) __attribute__((format(printf, 6, 7)));
+                    const char* format, ...) mxs_attribute((format(printf, 6, 7)));
 /**
  * Log an error, warning, notice, info, or debug  message.
  *

include/maxscale/modulecmd.h

@@ -256,7 +256,7 @@ bool modulecmd_call_command(const MODULECMD *cmd, const MODULECMD_ARG *args, jso
  * @param format Format string
  * @param ... Format string arguments
  */
-void modulecmd_set_error(const char *format, ...);
+void modulecmd_set_error(const char *format, ...) mxs_attribute((format (printf, 1, 2)));
 
 /**
  * @brief Get the latest error generated by the modulecmd system