Alpine Linux + Clang builder

[ac000]

As @hongzhidao suggested

The only question is if we need to add a BB test or not.

Do we want a BB with say, Alpine Linux + clang?

Yep, that's what I mean.

Apart from the extra resources and possible extra time to complete a run, I don't think having more clang coverage would be bad thing in general. AFAICT the only builders that currently use clang are the FreeBSD ones and the code analyser.

Originally posted by @ac000 in https://github.com/nginx/unit/issues/941#issuecomment-1710098546

[ac000]

@thresheek @andrey-zelenkov

To recap, this would be to provide coverage of building Unit under musl libc + clang.