XCode 4.3+ compatibility check-in

XCode 4.3 and later use a different location for SDKs. This check in
ensures the build checks for the new location as well as the old one.

Change-Id: I97884e5009f229f8b42e57a8feeb702b3a40a241
Signed-off-by: Al Sutton <al@funkyandroid.com>