[clang] [clang][Analyzer] Move checker 'alpha.unix.Errno' to 'unix.Errno'. (PR #69469)

[via cfe-commits]

https://github.com/DonatNagyE commented:

I'd say that the `readlink` modeling tweak is not a blocking issue; but the bug reports coming from "size is zero" corner case should be clarified (in a separate commit) before merging this.

As these are both easy to fix, I hope that we can move this checker out of alpha soon.

https://github.com/llvm/llvm-project/pull/69469