MSVC's qsort_s behaves similarly to sort_r. Unfortunately, qsort_s's
compare function has the "context"/"args" as its first argument. BSD's
qsort_r has a different order than GNU's qsort_r. Finally, C11 added
qsort_s's which look like GNU's gsort_r.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10989>