Enable optimizing compiler for V8 built-ins. Also fixes an issue uncovered in
x64 codegen.

R=danno@chromium.org, mstarzinger@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/34503003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17334 ce2b1a6d-e550-0410-aec6-3dcde31c8c00