Fix vm code base so that it can be built for --arch=simarm (no snapshot yet).

runtime/vm/constants_x64.h

Index: runtime/vm/constants_x64.h
===================================================================
--- runtime/vm/constants_x64.h	(revision 17245)
+++ runtime/vm/constants_x64.h	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2013, 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.
 
@@ -64,6 +64,12 @@
 };
 
 
+// Architecture independent aliases.
+typedef XmmRegister FpuRegister;
+const FpuRegister FpuTMP = XMM0;
+const int kNumberOfFpuRegisters = kNumberOfXmmRegisters;
+
+
 enum RexBits {
   REX_NONE   = 0,
   REX_B      = 1 << 0,