Added a workaround for Windows compilation problems related to V8EXPORT.

The underlying problem is a bit unclear, but at least this CL makes VS happy.

BUG=v8:2507

Review URL: https://codereview.chromium.org/12039037

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13470 ce2b1a6d-e550-0410-aec6-3dcde31c8c00