cffi-openmcl: fix test for cffi-features:darwin
cffi-openmcl: fix test for cffi-features:darwin

- Check for :darwin-target instead of :darwinppc-target.

dkochmanski/cffi,akovalenko/cffi,marsijanin/cffi,attila-lendvai/cffi,marsijanin/cffi,3b/cffi,marsijanin/cffi,akovalenko/cffi,stassats/cffi,kingcheez/cffi-cheez,cffi/cffi,dkochmanski/cffi,wesen/cffi,stassats/cffi,3b/cffi,kingcheez/cffi-cheez,akovalenko/cffi,dochang/cffi,dochang/cffi,kingcheez/cffi-cheez,wesen/cffi,mcna/cffi,3b/cffi,dochang/cffi,stassats/cffi,dkochmanski/cffi,cffi/cffi,mcna/cffi,cffi/cffi,attila-lendvai/cffi,wesen/cffi