mac: More flailing trying to get tests green on the bot.

TBR=mark
Review URL: https://codereview.chromium.org/12916006

git-svn-id: http://gyp.googlecode.com/svn/trunk@1598 78cadc50-ecff-11dd-a971-7dbc132099af
mac: Try to get tests green on xcode as well.

Two tests currently fail with
error: can't exec '/Developer/Library/Xcode/PrivatePlugIns/Xcode3Core.ideplugin/Contents/Frameworks/DevToolsCore.framework/Resources/clang' (No such file or directory)

TBR=mark
Review URL: https://codereview.chromium.org/12886015/

git-svn-id: http://gyp.googlecode.com/svn/trunk@1599 78cadc50-ecff-11dd-a971-7dbc132099af