Hi,

after several and several attempts to build  libffi on Mac OS X (10.6.8), I found a dmg that seems to work (!!) at

  http://code.google.com/p/rudix/downloads/detail?name=ffcall-1.10-2.dmg&can=2&q=label%3ARudix-2011

by using it I have been able to build (with port) CLISP with FFI :)

Hope it can be useful.

Alex