(define-foreign-library frobnicator (cffi-features:unix "/usr/lib/libfrobnicate.so"))
If it does, you should read Anton Kovalenko's blog, whether or not you use CFFI. (Reblogging this because the original was evidently not picked up by Planet Lisp.)
(define-foreign-library frobnicator (cffi-features:unix "/usr/lib/libfrobnicate.so"))