TF: Disable Win64 as a TurboFan target until calling conventions are sorted out.

R=danno@chromium.org
BUG=

Review URL: https://codereview.chromium.org/423713003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22760 ce2b1a6d-e550-0410-aec6-3dcde31c8c00