Hello,
I have ported CFFI to ABCL using the Java Native Access (JNA) library. This is a preliminary version that will have to be cleaned up and optimized, etc. Nevertheless, at this point it passes all of the relevant CFFI tests except one. Callbacks and shareable vectors are not implemented yet. The former seem to require functionality that is not yet present in ABCL, IIUC.
If anyone is interested in playing with this port, I have uploaded a patch to http://common-lisp.net/~loliveira/patches/cffi-abcl.diff. It requires trivial-features 0.5.
Cheers.