Reverts llvm/llvm-project#120450

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079

This patch adds the reentrent qsort entrypoint, qsort_r. This is done by
extending the qsort functionality and moving it to a shared utility
header. For this reason the qsort_r tests focus mostly on the places
where it differs from qsort, since they share the same sorting code.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D152467

Recent upstream changes to -fsanitize=function find more instances of
function type mismatches. One case is with the comparator passed to this
class. Libraries like boringssl will tend to pass comparators that take
pointers to varying types while this comparator expects to accept const
void pointers. Ideally those tools would pass a function that strictly
accepts const void*s to avoid UB, or we'd have something like qsort_r/s.

Differential Revision: https://reviews.llvm.org/D152322