Support OCaml 5 new Unix API names

[dra27]

The compiler is considering ensuring all symbols in the Unix library are prefixed caml_ for 5.0 (ocaml/ocaml#10926).

This requires:

• Pre-processing to select unix_exit or caml_unix_exit
• The removal of redundant declarations for functions in caml/socketaddr.h
• Version-based checking for the socket_domain_table and socket_type_table internal Unix symbols

[dra27]

The upstream OCaml PR was merged - please could someone kick GitHub actions?

[tmcgilchrist]

Re-running the analysis step to pickup dune 3.3.0 so this works on OCaml 5.0. Otherwise ocaml-ci should be working for this PR. @dra27

[smorimoto]

I just kicked GitHub Actions.

[dra27]

The tests require a release of base with janestreet/base#129 (comment) addressed, although temporarily pinning it also revealed a missing symbol shim.

With dra27@9d4f2b5b4, this passed ocaml-ci on 5.0

[raphael-proust]

Tested locally.

It just needs an entry in CHANGES. I'll push a commit for that.

Additionally, we could also add a check for 5.0.0~alpha0 in the CI. We currently already have 4.12+domains and 4.14+domains. Any reason not to do that? There's the fact that we'll want to modify it as the different alphas come in and then as 5.0.0 (non-alpha) is released. But the plus side is we can make sure that further PRs don't break anything.
I'm pushing a commit to that end. Let me know if you are ok with it.

[raphael-proust]

The ci is somewhat finicky because it's an alpha release. I'm merging this now and may address the CI later.

[dra27]

I wholeheartedly back adding 5.0 testing to CI 🙂