[tsan][test] Switch setitimer(ITIMER_REAL, ...) to setitimer(ITIMER_VIRTUAL, ...)

Followup to #85188.

Author: serge-sans-paille

compiler-rt/test/tsan/signal_thread.cpp

@@ -24,7 +24,7 @@ static void* thr(void *p) {
 int main() {
   struct sigaction act = {};
   act.sa_handler = &handler;
-  if (sigaction(SIGALRM, &act, 0)) {
+  if (sigaction(SIGVTALRM, &act, 0)) {
     perror("sigaction");
     exit(1);
   }
@@ -33,7 +33,7 @@ int main() {
   t.it_value.tv_sec = 0;
   t.it_value.tv_usec = 10;
   t.it_interval = t.it_value;
-  if (setitimer(ITIMER_REAL, &t, 0)) {
+  if (setitimer(ITIMER_VIRTUAL, &t, 0)) {
     perror("setitimer");
     exit(1);
   }