Use soname with major version for libffi on unix
Use soname with major version for libffi on unix

Use soname with major version for libffi on unix as advocated on 
http://lispcaveats.tumblr.com/post/13259176455/ffi-linking-against-shared-libraries.

dkochmanski/cffi,mcna/cffi,3b/cffi,cffi/cffi,attila-lendvai/cffi,cffi/cffi,mcna/cffi,stassats/cffi,stassats/cffi,dkochmanski/cffi,3b/cffi,attila-lendvai/cffi,cffi/cffi,dkochmanski/cffi,3b/cffi,stassats/cffi