Merged r14124, r14131 into 3.17 branch.

Ensure UseRegisterAtStart not used with fixed temp/return register

MIPS: Ensure UseRegisterAtStart not used with fixed temp/return register

BUG=chromium:201590

R=danno@chromium.org

Review URL: https://codereview.chromium.org/13527010

git-svn-id: https://v8.googlecode.com/svn/branches/3.17@14163 ce2b1a6d-e550-0410-aec6-3dcde31c8c00