Log Message:
Update to 3.12.1, syncing with current ocaml in pkgsrc and thereby
fixing the build.

Changes 3.12.0.0 -> 3.12.1.0:

- merge with OCaml 3.12.1

Changes 3.11.2.0 -> 3.12.0.0:

- merge with OCaml 3.12.0
- drop native ocamlducedoc
- fix memory leak issue in NS handling [Stefan Lampe]

Changes 3.11.1.0 -> 3.11.2.0:

- merge with OCaml 3.11.2
- build and install native-code plugin
- build ocamldoc library
- accept also ocaml_cmi_magic_number in objinfo