Add a new test to exercise async generators in the unwinder

Summary: Would have caught the bug in D20287874

Reviewed By: ricklavoie

Differential Revision: D20372127

fbshipit-source-id: bab667c8cecce7b66d38e1a11802d8bdbdda6213

Author: oulgen

hphp/test/slow/async/await_cpp_exception-2.php

@@ -0,0 +1,28 @@
+<?hh
+
+class C {
+  public static int $x = 0;
+}
+
+function handler($what, $fun) {
+  if ($fun == 'foo' && $what == 'exit') {
+    if (C::$x == 1) {
+      exit(1);
+    }
+    C::$x = 1;
+  }
+}
+
+async function foo() {
+  echo "enter\n";
+  $x = RescheduleWaitHandle::create(0, 0);
+  await $x;
+  yield null;
+}
+
+<<__EntryPoint>>
+async function main() {
+  fb_setprofile('handler');
+  foreach (foo() await as $_) {}
+  echo "NOOOOO!\n";
+}

hphp/test/slow/async/await_cpp_exception-2.php.expect

@@ -0,0 +1 @@
+enter