resolve unused variable warning on newer gcc

src/tools/opensc-notify.c

@@ -189,7 +189,10 @@ static int cancellation_fd[] = {-1, -1};
 
 void sig_handler(int sig) {
 	run_daemon = 0;
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-variable"
 	(void)write(cancellation_fd[1], &sig, sizeof sig);
+#pragma GCC diagnostic pop
 }
 
 static void *cancellation_proc(void *arg)