I've compiled a command-line tool (clipboard, written for OSX,
http://itp.stanford.edu/~zunger/clipboard.html). It uses NSPasteboard and
NSString AppKitAdditions, and since it was set up as just a plain tool, it was
not set up to link with -gui. It found headers for AppKit, so this only
resulted in errors at link time.
I don't think it should have found the AppKit headers, of course. This is
probably nothing to worry about now if -base and -gui will become frameworks,
and also because it's way too much work since AppKit/ and Foundation/ reside
in the same -I include path.