swift234

Make the CoreImage overlay (nee QuartzCore) work for both 10.11 and older OSs.

On OS X 10.10 and earlier, CoreImage is a sub-framework of QuartzCore.
Users of CoreImage use "import QuartzCore" and link against QuartzCore.

On OS X 10.11 (and in the OS X 10.11 SDK), CoreImage is a top-level
framework. Users of CoreImage use "import CoreImage" and would link against
CoreImage. Of course, QuartzCore continues to re-export CoreImage's API.

When backwards-deploying, we need to continue linking against QuartzCore,
but still need to bring in the overlay if you import CoreImage. That's
what this patch does.

rdar://problem/20196610

Swift SVN r28449