Flag --pretenure-call-new broken on MIPS.

A label in JSConstructStubHelper was in the wrong place.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/315963002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21674 ce2b1a6d-e550-0410-aec6-3dcde31c8c00