That combination should be correct. Essentially, elogind is the extracted-from-systemd tool to do what ConsoleKit used to do, so for a “modern” system with runit (or SysVinit or OpenRC) you should have elogind and not ConsoleKit, so your build options were correct. There is a known issue that makes the presence of shutdown menu options unreliable if you log out then log back in quickly, though. If the packaged version needs you to not be using elogind then it’s probably been built with CK support. Once I get round to playing with Void I’ll try to figure that out.
That’s certainly a fair argument but it’s not the commonly accepted wisdom and, in any case, should be up to the sysadmin to decide. SLiM should not (and does not, intentionally) impose anything either way.
What I meant was that, on Gentoo and Devuan, cmake automatically finds the correct X11_Xmu_INCLUDE_PATH, presumably because it’s been registered in some way. That might be via pkgconfig or it might be something else. I’m not familiar enough with cmake’s foibles to tell you why it didn’t work for you, but my guess would be there’s a post-install step needed somewhere.