PR#7217: Unix.symlink does not raise on Mingw64.
PR#7217: Unix.symlink does not raise on Mingw64.

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