[libc] Temporarily suppress -fsanitize=function for qsort comparator

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