by working around slightly "wrong" definition of uintptr_t on Mac OS X.
  Verified that this works on both ia32 and x64 on Linux and Mac OS X.

Review URL: http://codereview.chromium.org/115252

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00