How about a license that was "MIT, unless you're Apple in which case it's GPL"? Wouldn't that be compatible with the GPL? You would be effectively barring Apple from using it, as they won't use GPL code inside `PhotoLibraryServices.framework`.
IANAL, but I don't think that would be GPL compatible. You're only explicitly allowing Apple to use it under the GPL, not other parties. And even though "unless you're Apple in which case it's the GPL" involves the GPL, it's still a licensing restriction which is not included in the GPL.
