[asan] De-flake one test.

This change replaces an in-test timeout with an unconditional blocking wait.
It speeds up normal execution significantly at the cost of hanging up indefinitely
in case of a failure. This is a very specific regression test and we don't
expect any failures in the future.

Another approach ould be increasing the timeout to ~8 seconds, which seems too
much for a lit test.

llvm-svn: 217870

compiler-rt/test/msan/fork.cc

@@ -70,8 +70,8 @@ void test() {
   if (pid) {
     // parent
     __atomic_store_n(&done, 1, __ATOMIC_RELAXED);
-    usleep(1000000);
-    kill(pid, SIGKILL);
+    pid_t p;
+    while ((p = wait(NULL)) == -1) {  }
   } else {
     // child
     child();