The original question was about using libPerformance on OSX (one of a few
libraries I've written. ad a few others have contributed to, primarily for
server process work, and contributed to the FSF).
This was not about using the GNUstep core libraries.
Now you might well want to use libPerformance with the Apple Foundation if you
want to write a better program on Cocoa, since it contains functionality Apple
don't provide.
In fact, you might well want to build base with the Apple Foundation (in which
case it should just build the base additions library) for the extra classes we
provide which are not available normally on OSX.
And of course, if you want to build these libraries for use on OSX, would also
want to install gnustep-make (to build them).
So in fact there are good technical reasons to want to build most parts of
GNUstep on OSX even if you intend to use the Apple native runtime and
Foundation frameworks, and this is what the original poster was asking about.
I don't own a copy of OSX 10.7, but perhaps I should buy one in order to port
at least the non-gui parts of GNUstep to it.