[Caml-list] First release candidate for OCaml 5.1.0

[Florian Angeletti <florian.angeletti@inria.fr>]

Dear OCaml users,

The release of OCaml 5.1.0 is imminent.
As a final step, we are publishing a release candidate to check that 
everything is in order before the release in the upcoming week(s).

If you find any bugs, please report them on [OCaml's issue 
tracker](https://github.com/ocaml/ocaml/issues).

Compared to the beta release, this release candidate contains one safe 
runtime fix, and two configuration tweaks.

The full change log for OCaml 5.1.0 is available [on 
GitHub](https://github.com/ocaml/ocaml/blob/5.1/Changes)
A short summary of the changes since the beta release is also available 
below.

Happy hacking,
Florian Angeletti for the OCaml team.

Installation Instructions
-----------------------------------

The base compiler can be installed as an opam switch with the following 
commands on opam 2.1 and later:

     opam update
     opam switch create 5.1.0~rc1

The source code for the release candidate is also directly available on:

* GitHub: https://github.com/ocaml/ocaml/archive/5.1.0-rc1.tar.gz
* OCaml archives at Inria: 
https://caml.inria.fr/pub/distrib/ocaml-5.1/ocaml-5.1.0~rc1.tar.gz

### Fine-Tuned Compiler Configuration

If you want to tweak the configuration of the compiler, you can switch 
to the option variant with:

     opam update
     opam switch create <switch_name> ocaml-variants.5.1.0~rc1+options 
<option_list>

where <option_list> is a comma-separated list of `ocaml-option-*` 
packages. For instance, for a `flambda` and `no-flat-float-array` switch:

     opam switch create 5.1.0~rc1+flambda+nffa 
ocaml-variants.5.1.0~rc1+options ocaml-option-flambda 
ocaml-option-no-flat-float-array

All available options can be listed with `opam search ocaml-option`.


Changes Since the Beta Release
----------------------------------------------

### Bug Fix

- #12445(https://github.com/ocaml/ocaml/issues/12445): missing GC root 
registrations in runtime/io.c
   (Gabriel Scherer, review by Xavier Leroy and Jeremy Yallop)

### Configuration Fix (openBSD)

- #12372(https://github.com/ocaml/ocaml/issues/12372): Pass option 
-no-execute-only to the linker for OpenBSD >= 7.3
   so that code sections remain readable, as needed for closure marshaling.
   (Xavier Leroy and Anil Madhavapeddy, review by Anil Madhavapeddy and
   Sébastien Hinderer)

### Tool Fix (ocamlmktop)

* #11745, #12358(https://github.com/ocaml/ocaml/issues/12358): Debugger 
and toplevels: embed printer types rather than
   reading their representations from topdirs.cmi at runtime.
   This change also removes the ocamlmktop initialization module introduced
   in [#11382](https://github.com/ocaml/ocaml/issues/11382) which was no 
longer useful.
   This change breaks toplevel scripts relying on the visibility of 
`Topdirs`
   in the initial toplevel environment without loading `topfind`.
   Since the opam default `.ocamlinit` file loads `topfind`, it is expected
   that only scripts run with `ocaml -noinit` are affected.
   For those scripts, accessing `Topdirs` now requires the `compiler-libs`
   directory to be added to the toplevel search path with
   ```
     #directory "+compiler-libs";;
   ```
  as was already the case for the other modules in the toplevel interface
  library.
  (Sébastien Hinderer, review by Florian Angeletti, Nicolás Ojeda Bär and
  Gabriel Scherer)

### Documentation Changes

- #12201(https://github.com/ocaml/ocaml/issues/12201): in the tutorial 
on modules, replace priority queue example by
   a simpler example based on FIFO queues.
   (Xavier Leroy, review by Anil Madhavapeddy and Nicolás Ojeda Bär).

- #12352(https://github.com/ocaml/ocaml/issues/12352): Fix a typo in the 
documentation of Arg.write_arg
   (Christophe Raffalli, review by Florian Angeletti)