On x64 the return from debug break slot did not pop off the return address.

TBR=ager@chromium.org
Review URL: http://codereview.chromium.org/2731002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4823 ce2b1a6d-e550-0410-aec6-3dcde31c8c00