Unbreak "os" stuff in shared d8 builds.

Note that "os" still has no properties on Windows, but at least it's there.

BUG=v8:3407
LOG=y
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/356843005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22058 ce2b1a6d-e550-0410-aec6-3dcde31c8c00