Compile V8 with extra optimization in GN Release mode.

This matches the GYP build which does 'optimize': 'max' on the corresponding targets.

R=jochen@chromium.org

Review URL: https://codereview.chromium.org/567073003

Patch from Brett Wilson <brettw@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23952 ce2b1a6d-e550-0410-aec6-3dcde31c8c00