CI: Do the CMake native debug build from an Autotools `make dist`
We officially release dbus in the form of Autotools make dist tarballs,
but people who have downloaded those tarballs should be able to choose
the CMake build system. Our CI should assert that they can.
(The Autotools debug build already does a make distcheck, which
asserts that tarball releases can be used for an Autotools build.)
Signed-off-by: Simon McVittie smcv@collabora.com Resolves: #255 (closed)