Allow mixing of thread offsets between 32 and 64bit architectures.

Begin a more full implementation x86-64 REX prefixes.
Doesn't implement 64bit thread offset support for the JNI compiler.

Change-Id: If9af2f08a1833c21ddb4b4077f9b03add1a05147
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index a8da2f8..f016189 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -576,7 +576,7 @@
   // objects. We can't supply a thread group yet; it will be fixed later. Since we are the main
   // thread, we do not get a java peer.
   Thread* self = Thread::Attach("main", false, NULL, false);
-  CHECK_EQ(self->thin_lock_thread_id_, ThreadList::kMainThreadId);
+  CHECK_EQ(self->GetThreadId(), ThreadList::kMainThreadId);
   CHECK(self != NULL);
 
   // Set us to runnable so tools using a runtime can allocate and GC by default