This patch introduces global once per-process initialization and moves
the OS and CPU setup there. This makes CPU features isolate-independent.

Review URL: http://codereview.chromium.org/6670119

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7462 ce2b1a6d-e550-0410-aec6-3dcde31c8c00