ARM: build fix for r19380.

This commit fixes the debug build on Linux with gcc 4.6.3 and 4.7.2.

Port r19381 (5476e11b)

BUG=
R=dcarney@chromium.org, plind44@gmail.com

Review URL: https://codereview.chromium.org/167523003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19398 ce2b1a6d-e550-0410-aec6-3dcde31c8c00