Unbreak build with clang.

It's unclear whether it's a clang bug or our code is wrong, to be
verified later...

TBR=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/438323002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22878 ce2b1a6d-e550-0410-aec6-3dcde31c8c00