OCamlMakefile: apply some patches from fdopen/opam-repository-mingw for building under windows
OCamlMakefile: apply some patches from fdopen/opam-repository-mingw for building under windows

dra27/merlin,rgrinberg/merlin,ocaml/merlin,fxfactorial/merlin,fxfactorial/merlin,the-lambda-church/merlin,the-lambda-church/merlin,ocaml/merlin,ocaml/merlin,dra27/merlin,rgrinberg/merlin,fxfactorial/merlin,fxfactorial/merlin,rgrinberg/merlin,dra27/merlin,the-lambda-church/merlin,ocaml/merlin,dra27/merlin,rgrinberg/merlin