Implement flooring division by a constant via truncating division by a constant.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/204583002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20123 ce2b1a6d-e550-0410-aec6-3dcde31c8c00