Merge x64 minus-zero fix (bleeding_edge r5631) to 2.2 branch.

TBR=whesse@chromium.org
Review URL: http://codereview.chromium.org/3858001

git-svn-id: http://v8.googlecode.com/svn/branches/2.2@5634 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
3 files changed