Fix compilation on win64

TBR=bmeurer@chromium.org
LOG=n
BUG=none

Review URL: https://codereview.chromium.org/613093004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24440 ce2b1a6d-e550-0410-aec6-3dcde31c8c00