Fix dev-mode compiler warning about gnu_printf

(related to ASTERISK-19575)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@361039 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/manager.h

@@ -262,7 +262,7 @@ struct ast_variable *astman_get_variables(const struct message *m);
 void astman_send_error(struct mansession *s, const struct message *m, char *error);
 
 /*! \brief Send error in manager transaction (with va_args support) */
-void astman_send_error_va(struct mansession *s, const struct message *m, const char *fmt, ...);
+void __attribute__((format(printf, 3, 4))) astman_send_error_va(struct mansession *s, const struct message *m, const char *fmt, ...);
 
 /*! \brief Send response in manager transaction */
 void astman_send_response(struct mansession *s, const struct message *m, char *resp, char *msg);