Revert "fix: set the SA_ONSTACK flag"

Author: Pithikos

thpool.c

@@ -349,7 +349,7 @@ static void* thread_do(struct thread* thread_p){
 	/* Register signal handler */
 	struct sigaction act;
 	sigemptyset(&act.sa_mask);
-	act.sa_flags = SA_ONSTACK;
+	act.sa_flags = 0;
 	act.sa_handler = thread_hold;
 	if (sigaction(SIGUSR1, &act, NULL) == -1) {
 		err("thread_do(): cannot handle SIGUSR1");