If ocamlbuild is at a version that doesn't have the fix yet, how about applying the first two patches of this MR?  https://github.com/ocaml/ocamlbuild/pull/302/commits

Thanks for your work on this!

Le 30 août 2020 20:36:12 GMT-04:00, Brett Gilio <brettg@gnu.org> a écrit :
>Hey all,
>
>I am currently working on a new branch wip-ocaml to try and get our
>ocaml packages to build against latest 4.11
>
>For some reason, when building ocamlbuild against 4.11 there is a race
>condition which is introduced where cudf fails to build. I can not seem
>to decipher how to resolve the issue, though.
>
>--8<---------------cut here---------------start------------->8---
>Failure:
>Error during command "mkdir
>/tmp/guix-build-ocaml-cudf-0.9.drv-0/cudf-0.9/_build":
>Ocamlbuild_pack.My_std.Exit_with_code(10).
>make: *** [Makefile:61: _build/cudf.cma] Error 2
>--8<---------------cut here---------------end--------------->8---
>
>I did manage to find this relevant issue though:
>https://github.com/ocaml/ocamlbuild/issues/300.
>
>Any help would be appreciated.
>
>Brett Gilio