Add patches/ocaml-system/gen_ocaml_config.ml.in.after-5.4.0

[kit-ty-kate]

Required for ocaml/opam-repository#28455

[dra27]

This is very timely, thanks! Relocatable needs to update one of the other gen_ocaml_config.ml scripts, and one of the things I'd dealt with is the very strange situation where we appear to be making this "archive" repository the primary location of development for some of these scripts 😁

[dra27]

(the commits are in dra27/ocaml#ocaml-config - I'll do a PR for that relatively soon... GitHub's ridiculous display of commits in date order rather than graph order makes looking at that branch very strange)

[mseri]

Should we wait for an update to this PR then?

[dra27]

Yes, please! I'm also not instantly certain that the change is a good idea (but that also means I'm not instantly certain that it's a bad idea either!!), so I'd await @Octachron's opinion. I have encountered in my own testing before the issue here with ocaml-system, but my instinct then was not to change ocaml-system. What's different now, of course, is that ocaml-system is very de-prioritised since opam 2.4 for normal users.