qsort shares the same C language bug as mem*. Two of our calls may see
zero-length lists. This trips UBSan.

Change-Id: Id292dd277129881001eb57b1b2db78438cf4642e
Reviewed-on: https://boringssl-review.googlesource.com/c/34447
Reviewed-by: Adam Langley <agl@google.com>