shells/zsh: cache the utx.active location

On fresh jails or chroot the /var/run/utx.active might not exist (like
in poudriere for example) but configure script is looking for its
existance to determine its existance and activate the build of the
utmx logging feature internally.

Caching it makes the configure script always build the logging features.

While here, make ZSH_VER use the distversion, which fixes the usecase of
building snapshots of zsh via the port.

PR: 268714
Reported by: okiddle@yahoo.co.uk