Define _XOPEN_SOURCE for NetBSD

This is backported from
https://github.com/antirez/redis/commit/289942b6259670fe3dcfaffdd0135c27f14c61c0
Upgrade sds to latest version

SDS is now broken out of Redis into its own project, so include
the latest version from the SDS repo.

This is a backport of the Redis commit doing the same to the bundled hiredis:
https://github.com/antirez/redis/commit/320fa02b9b48ee1c63d88db6344fc0d328e24853
Add missing license and copyright for adapters

This is a backport of
https://github.com/antirez/redis/commit/d01aad329c259a7276c448cee6696b04dfa6f8c1