Fix AttachCurrentThread to use the right thread group.

Change-Id: I9818845c005563d894a571edc4f9be9862312380
diff --git a/src/compiler.cc b/src/compiler.cc
index 72cabbf..b56fd49 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -921,7 +921,7 @@
     WorkerThread* worker = reinterpret_cast<WorkerThread*>(arg);
     Runtime* runtime = Runtime::Current();
     if (worker->spawn_) {
-      runtime->AttachCurrentThread("Compiler Worker", true);
+      runtime->AttachCurrentThread("Compiler Worker", true, NULL);
     }
     Thread::Current()->SetState(Thread::kRunnable);
     worker->Run();