Add Dune package management compatibility patch for ocamlbuild

[Sudha247]

Adds a patch to ocamlbuild to maintain compatibiltiy with dune package management, extracted from our branch at https://github.com/gridbugs/ocamlbuild/tree/0.16.1%2Bdune. This will enable the package to work when a project that requires this as a dependency is built with Dune package management. It will also continue working with opam. Some of this has been upstreamed to ocaml/ocamlbuild but not released yet.

[avsm]

I couldn't find any explanation of what the actual incompatibility is anywhere. What's different with dune pkg management and opam here?

[Sudha247]

The main difference is Dune package management doesn't support symlinks yet. The issue is described here: ocaml/dune#12736. My bad, I meant to link it here.

This patch is adapted from one of the links in the issue: ocaml/ocamlbuild@master...gridbugs:ocamlbuild:0.16.1+dune