Fix float varargs promotion.
Fix float varargs promotion.

- Convert floats to doubles in foreign-funcall-varargs. Test
  DEFCFUN.VARARGS.FLOAT now passes.

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