CMake builds from tarball releases are not tested
If our aim is for it to be possible to build official dbus tarball releases (which come from Autotools
make dist) with CMake, then we should probably change at least one of the CMake CI jobs in
tools/ci-build.sh so that instead of building with CMake directly from git, it does a
make dist with Autotools, unpacks the resulting tarball, and uses CMake to build that.
(Doing an Autotools build from a tarball release is already exercised in CI, because
make distcheck does that for us.)