Update libffi-unix.lisp
Update libffi-unix.lisp

Added functionalities for freebsd os.
stassats/cffi,dkochmanski/cffi,3b/cffi,dkochmanski/cffi,stassats/cffi,dkochmanski/cffi,3b/cffi,mcna/cffi,attila-lendvai/cffi,stassats/cffi,cffi/cffi,cffi/cffi,cffi/cffi,attila-lendvai/cffi,mcna/cffi,3b/cffi