Kamil Rytarowski authored Mar 12, 2018 and Thomas Guillem committed Mar 13, 2018

Disable calls that are already handled by the NetBSD libc:
 - popcount(3)
 - popcountll(3)
 - bswap16(3)
 - bswap32(3)
 - bswap64(3)

These functions were renamed to vlc_* in HEAD (vlc-4.x) and since
they are set in stone in the stable releases use ifdef NetBSD here.

This corrects fatal build issues reported on NetBSD.

Signed-off-by: Thomas Guillem <thomas@gllm.fr>