Please add libsystemd-static

Thanks for packaging this library, which is unfortunately needed to compile some software, even though the system contains no systemd at all.

Currently `-Dstatic-libsystemd=false` is set, but I need the static library.

Could you please add a `libsystemd-static` package and provide information on how to build that one instead?

Reference: https://github.com/probonopd/static-tools/pull/47