'inconsistent assumptions over implementation Unix' with Ocaml 4.04

[gautierhattenberger]

Some distribution's packages are broken with Ocaml 4.04 with the following error:

+ ocamlfind ocamlopt unix.cmxa -I /usr/lib64/ocaml/ocamlbuild /usr/lib64/ocaml/ocamlbuild/ocamlbuildlib.cmxa -linkpkg myocamlbuild.ml /usr/lib64/ocaml/ocamlbuild/ocamlbuild.cmx -o myocamlbuild
File "myocamlbuild.ml", line 1:
Error: Files /usr/lib64/ocaml/ocamlbuild/ocamlbuildlib.cmxa
       and /usr/lib64/ocaml/unix.cmxa
       make inconsistent assumptions over implementation Unix
Command exited with code 2.

This is reported on Fedora 26 (https://bugzilla.redhat.com/show_bug.cgi?id=1528513) and I can confirm it for Ubuntu 17.10 as well.

Is this a pure distributions issue or something wrong in the Ocaml buildsystem ?

[kit-ty-kate]

This is most likely a distributions issue as the source code doesn't contain any compiled files.
My guess is that they updated their ocaml package but not the package that contains the ocamlbuild library.