Otherwise find_library is unable to lookup the XCTest framework which
is not located in the SDK serach path:
In the 10.10 SDK the SDK frameworks are located here:
$DEVELOPER_DIR/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/System/Library/Frameworks
whereas the Platform SDKs are located here:
$DEVELOPER_DIR/Platforms/MacOSX.platform/Developer/Library/Frameworks
Signed-off-by: Gregor Jasny <gjasny@googlemail.com>