Meson option enhancements
The two commits are fairly independant, but under the same theme:
- first commit makes the message printed at meson time to reflect what is actually built, rather than the option default values (been annoying me for a while to have elogind = true in that message when I don't have elogind...)
- second commit implements some sort of auto/true/false mechanism, that by default tries to build whatever we have, but if someone explicitely sets meson -Denable_foo=true will fail when foo is not found. This should not break either default (true was technically auto before) nor explicit configs as -Denable_foo=false is the same syntax. Happy to remove this commit if it is not welcome but this usually makes sense to do.