Unbreak non-SSE2 ia32 platforms.

Improved register usage a bit on the way.

Review URL: https://codereview.chromium.org/12082043

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13534 ce2b1a6d-e550-0410-aec6-3dcde31c8c00