archive_utility_string_sort: Use qsort directly

archive_utility_string_sort: Use qsort directly

The utility function "archive_utility_string_sort" is a custom qsort
implementation. Since qsort is specified in C11 and POSIX.1-2008
which libarchive is based on, use system's qsort directly.

The function is not used directly in libarchive, so this is a good
way to save around 500 bytes in resulting library without breaking
compatibility for any user of this function (none found).

Also allows more than UINT_MAX entries which previously were limited
by data type and (way earlier) due to recursion.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>