OCaml: transient update of the stack to version 4.07.1

This is the first step in modernizing our OCaml ports infrastructure,
as we had accumulated substantial technical debt over the years when
many of its consumer ports had not received proper care and updates.

It is currently considered as the lowest supported version (baseline)
in majority of open-source OCaml projects, which would help to pull
up other ports, e.g. `devel/ocaml-dune' in smaller, manageable pieces.

For conservative hackers among us and for compatibility with RHEL 8
which is also on it, having 4.07 in the tree would allow users stick
to that package (pkg lock it) if needed.

PR: 250408, 262781
Exp-run by: antoine