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

[Lukas Bergdoll via llvm-commits]

Voultapher wrote:

@michaelrj-google from what I know Google has extensive performance monitoring in production, once this change reaches systems it would be interesting to get some feedback if it actually improves real world cases. A lot of the perf critical sorting is done via vqsort as far as I understand, but this could still have some impact would be great to know - with the appropriate lack of details of course.

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