Since hydrogen will try to merge phi-inputs using registers, even if
the values are spilled, we cannot mark LGoto as double clobbering
instruction.

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/23068038

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16671 ce2b1a6d-e550-0410-aec6-3dcde31c8c00