Implement Math.ceil via Math.floor.

This way we get all the Crankshaft goodness and avoid always going
through the runtime: Less code + even some small speedup in Kraken.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/88053002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18072 ce2b1a6d-e550-0410-aec6-3dcde31c8c00