Having GitHub checks on macos is important for not inadvertently breaking the builds.

GitHub has announced that macos-12 runners will be deprecated in December, 2024, with some temporary failures expected in November, 2024. See https://github.blog/changelog/2024-08-19-notice-of-upcoming-deprecations-and-breaking-changes-in-github-actions-runners/ thus making these checks unavailable after that date.

As a consequence is mandatory to upgrade the GitHub runners to XCode 14 or greater before December, 2024, while still keeping compatibiliity with previous build systems.

The build mechanism should include a configuration flag `--enable-xcode14` that makes it possible to

- build JDK11 on both existing pipelines (XCode 13 and earlier, without the `--enable-xcode14` flag)
- at least build and run tier1 tests on XCode 14 and later (with the `--enable-xcode14` configuration flag).

Future enhancements may expand the usage of XCode 14 to other parts of the codebase (executing tier2 tests, etc.).