[libc] [llvm] [libc] Improve qsort (PR #120450)

[Schrodinger ZHU Yifan via llvm-commits]

SchrodingerZhu wrote:

@Voultapher can u make a quick fix to the build error? If you are not available right now, I will need to revert the patch and reland this with your fix.

https://github.com/llvm/llvm-project/pull/120450