Move generated math methods from platform to codegen

BUG=none
R=mstarzinger@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/269823006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21163 ce2b1a6d-e550-0410-aec6-3dcde31c8c00