mac: Try to get the two new clang-specific tests pass on the gyp bot (Xcode 4.2)

Not sure if 4.2 can target 10.7, so maybe it won't work.

TBR=mark
Review URL: https://codereview.chromium.org/12869006

git-svn-id: http://gyp.googlecode.com/svn/trunk@1596 78cadc50-ecff-11dd-a971-7dbc132099af
mac: Try to get test/mac/gyptest-sdkroot.py to pass on both bots and dev boxes.

Fallout from r1594.

TBR=mark
Review URL: https://codereview.chromium.org/12901002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1597 78cadc50-ecff-11dd-a971-7dbc132099af