This is a reland of 22945, which failed to build on Windows due to
(some versions of?) Visual Studio lacking copysign().

R=rossberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/448093002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22977 ce2b1a6d-e550-0410-aec6-3dcde31c8c00