Add OpenMP based parallelization also to qsort

[game-difficulty]

Thank you for your great work on x86-simd-sort! I noticed that on May 29, a pull request titled "Adds OpenMP based parallelization to key-value sorting" was merged, which added OpenMP-based parallelization to key-value sorting and brought significant performance improvements for large arrays.

However, it seems that qsort in the library does not yet include similar thread-level parallelization.

Adding OpenMP-based parallelization to qsort could yield significant performance improvements. Would it be possible to extend the same parallelization approach to qsort in the future?

[r-devulap]

@game-difficulty I think that should be possible. I am on travel right now, we will look into it once I am back in a few weeks.