Update Makefile.nt so that ocamlnat compiles for non-Cygwin Windows ports.
Update Makefile.nt so that ocamlnat compiles for non-Cygwin Windows ports.

Rules were either missing or not up-to-date.

yunxing/ocaml,msprotz/ocaml,yunxing/ocaml,msprotz/ocaml,msprotz/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,eliberis/ocaml,eliberis/ocaml,yunxing/ocaml,msprotz/ocaml,eliberis/ocaml,yunxing/ocaml,msprotz/ocaml,eliberis/ocaml,eliberis/ocaml,gerdstolpmann/ocaml,gerdstolpmann/ocaml,yunxing/ocaml