Check for negative zero in floor when compiling with MSVC.

R=danno@chromium.org
BUG=v8:3477
LOG=N

Review URL: https://codereview.chromium.org/429603003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22674 ce2b1a6d-e550-0410-aec6-3dcde31c8c00