[libc] [llvm] [libc] Improve qsort (with build fix) (PR #121482)

[Lukas Bergdoll via llvm-commits]

Voultapher wrote:

Not sure on the git approach here, should I do the original commits or revert the revert and add just add the new commit?

https://github.com/llvm/llvm-project/pull/121482