Ensure UseRegisterAtStart not used with fixed temp/return register

R=vegorov@chromium.org
BUG=chromium:201590

Review URL: https://codereview.chromium.org/13527007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14124 ce2b1a6d-e550-0410-aec6-3dcde31c8c00