- add BR pkgconfig(libsystemd) for the rewritten systemd support
and force building with it

- Update to 6.0.1
* https://raw.githubusercontent.com/antirez/redis/6.0.1/00-RELEASENOTES
* XCLAIM AOF/replicas propagation fixed.
* Client side caching: new NOLOOP option to avoid getting
notified about changes performed by ourselves.
* ACL GENPASS now uses HMAC-SHA256 and have an optional
"bits" argument. It means you can use it as a general purpose
"secure random strings" primitive!
* Cluster "SLOTS" subcommand memory optimization.
* The LCS command is now a subcommand of STRALGO.
* Meaningful offset for replicas as well. More successful
partial resynchronizations.
* Optimize memory usage of deferred replies.
* Faster CRC64 algorithm for faster RDB loading.
* XINFO STREAM FULL, a new subcommand to get the whole stream
state.
* CLIENT KILL USER .
* MIGRATE AUTH2 option, for ACL style authentication support.
* Other random bugfixes.