Building CoreFoundation.framework from swift-corelibs-foundation on macOS

Right now, CF exists mostly as an implementation detail of Swift Foundation. You can conceivably build it for other uses, but we haven’t put any work into sustainably supporting this for any platform other than Linux. We welcome contributions this way, but note that on Darwin, modulo for the very narrow scope of building Swift Foundation for testing, I think it’s safe to say we really, really would prefer people use the installed CF instead.