Make it clear that GCMole depends on Clang 2.9 currently.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/13950017

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14393 ce2b1a6d-e550-0410-aec6-3dcde31c8c00