Begins work on ARM64, first assembler test.

runtime/vm/runtime_entry_arm64.cc

Index: runtime/vm/runtime_entry_arm64.cc
===================================================================
--- runtime/vm/runtime_entry_arm64.cc	(revision 0)
+++ runtime/vm/runtime_entry_arm64.cc	(revision 0)
@@ -0,0 +1,24 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/globals.h"
+#if defined(TARGET_ARCH_ARM64)
+
+#include "vm/runtime_entry.h"
+
+#include "vm/assembler.h"
+#include "vm/simulator.h"
+#include "vm/stub_code.h"
+
+namespace dart {
+
+#define __ assembler->
+
+void RuntimeEntry::Call(Assembler* assembler, intptr_t argument_count) const {
+  UNIMPLEMENTED();
+}
+
+}  // namespace dart
+
+#endif  // defined TARGET_ARCH_ARM64