[clang] [libcxx] [llvm] Triple::normalize: Use none as OS for XX-none-ABI (PR #89638)

[Peter Waller via cfe-commits]

https://github.com/peterwaller-arm requested changes to this pull request.

Thanks for doing this and waiting for RFC comments.

I think this can be merged, the one thing which needs fixing is removing the change I've commented on so that the picolibc builder can succeed (it uses a version of clang on the builder, which @DavidSpickett will update at the right time).

https://github.com/llvm/llvm-project/pull/89638