I see this also, on Leopard x86. The linker error is not printed on
Tiger PPC.  At least, the ctypes test suite does work ok so it may be
that it can be ignored.

Googling for this error, I find that it may be related to linker changes
that Apple has made.
One suggestion I found was to link with ld_classic instead of ld;
another was to pass the -dynamic flag instead of -bundle.  However, I do
not known how this can be done in setup.py.

The libffi sources in Python svn were copied from the PyObjC sources;
maybe Ronald has a clue?