Merged r17566 into 3.22 branch.

Fix clang debug build.

TBR=ulan@chromium.org
BUG=v8:3065

Review URL: https://codereview.chromium.org/111583003

git-svn-id: https://v8.googlecode.com/svn/branches/3.22@18417 ce2b1a6d-e550-0410-aec6-3dcde31c8c00