Support static_funptr coercions.
Support static_funptr coercions.

yallop/ocaml-ctypes,dsheets/ocaml-ctypes,whitequark/ocaml-ctypes,whitequark/ocaml-ctypes,sjfloat/ocaml-ctypes,whitequark/ocaml-ctypes,ocamllabs/ocaml-ctypes,dsheets/ocaml-ctypes,sjfloat/ocaml-ctypes,dsheets/ocaml-ctypes,sjfloat/ocaml-ctypes,yallop/ocaml-ctypes,ocamllabs/ocaml-ctypes