openrc-shutdown: mark handler as noreturn, use _unused macro

src/openrc-shutdown/broadcast.c

@@ -44,11 +44,7 @@ static sigjmp_buf jbuf;
  *	Alarm handler
  */
 /*ARGSUSED*/
-# ifdef __GNUC__
-static void handler(int arg __attribute__((unused)))
-# else
-static void handler(int arg)
-# endif
+_noreturn static void handler(int arg _unused)
 {
 	siglongjmp(jbuf, 1);
 }