Fix Win64 build

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/12221012

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13594 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix Win64. It still cares about the actual registers behind scratch1/scratch2

Review URL: https://chromiumcodereview.appspot.com/12211011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13595 ce2b1a6d-e550-0410-aec6-3dcde31c8c00