Allow for compiling with xcode 5.1 (which doesn't have gcc anymore)

BUG=none
R=jkummerow@chromium.org, machenbach@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/196983006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19917 ce2b1a6d-e550-0410-aec6-3dcde31c8c00