Use stable sort to make sure bench with TB yields same results everywhere.

Use stable sort to make sure bench with TB yields same results everywhere.

std::sort() is not stable so different implementations can produce different results:
use the stable version instead.

Observed for '8/6k1/5r2/8/8/8/1K6/Q7 w - - 0 1' yielding different bench results for gcc and MSVC
and 3-4-5 syzygy TB prior to this patch.

closes https://github.com/official-stockfish/Stockfish/pull/3083

No functional change.