multiplication by its inverse.

In optimized builds GCC does this on its own, but this may be useful
when using other compilers.
Review URL: http://codereview.chromium.org/11524

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@805 ce2b1a6d-e550-0410-aec6-3dcde31c8c00