Add amd64 to GuessArchitecture

Patch by Ryan Dahl <coldredlemur@gmail.com>, see http://codereview.chromium.org/1707013.
Review URL: http://codereview.chromium.org/1732016

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4523 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/utils.py

@@ -71,6 +71,8 @@ def GuessArchitecture():
     return 'ia32'
   elif id == 'i86pc':
     return 'ia32'
+  elif id == 'amd64':
+    return 'ia32'
   else:
     return None