Fix Windows build of defaults.cc.

BUG=None
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/24762002

Patch from Ross McIlroy <rmcilroy@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16968 ce2b1a6d-e550-0410-aec6-3dcde31c8c00