Ocaml 4.12.0, first beta

[Octachron]

This PR adds the package for the first beta for OCaml 4.12.0 .

On the compiler side, this is a quiet release with 3 bug fixes:

• one error message fix
• one performance regression fix for immediate objects
• one gc control fix (which fix some performance regression in Coq present since 4.08)

The major change is on the standard library side with two functions postponed to avoid some potential conflicts with extlib.

Postponed features

• 9533, 10105, 10127 : Added String.starts_with and String.ends_with.
  (Bernhard Schommer, review by Daniel Bünzli, Gabriel Scherer and
  Alain Frisch)

Additional bug fixes

• 9096, 10096: fix a 4.11.0 performance regression in classes/objects
  declared within a function
  (Gabriel Scherer, review by Leo White, report by Sacha Ayoun)

• 9326, 10125: Gc.set incorrectly handles the three custom_* fields,
  causing a performance regression
  (report by Emilio Jesús Gallego Arias, analysis and fix by Stephen Dolan,
  code by Xavier Leroy, review by Hugo Heuzard and Gabriel Scherer)

• 10106, 10112: some expected-type explanations where forgotten
  after some let-bindings
  (Gabriel Scherer, review by Thomas Refis and Florian Angeletti,
  report by Daniil Baturin)

[kit-ty-kate]

Thanks a lot! 🎉

[camelus]

Commit: 71e237a

@Octachron has posted 39 contributions.

🌤️ opam-lint warnings 71e237a

• ocaml.4.12.0 has some warnings:

  • warning 56: It is discouraged for non-compiler packages to use 'setenv:'

• ocaml.4.13.0 has some warnings:

  • warning 56: It is discouraged for non-compiler packages to use 'setenv:'

• These packages passed lint tests: ocaml-base-compiler.4.12.0~beta1, ocaml-variants.4.12.0~beta1+options

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☀️ Installability check (+2)

• new installable packages (2): ocaml-base-compiler.4.12.0~beta1 ocaml-variants.4.12.0~beta1+options

---

🌤️ 2 ignored non-opam files:

• packages/ocaml-base-compiler/ocaml-base-compiler.4.12.0~beta1/files/ocaml-base-compiler.install
• packages/ocaml-variants/ocaml-variants.4.12.0~beta1+options/files/ocaml-variants.install