gitlab: avoid building libvirt twice and running syntax-check twice

gitlab: avoid building libvirt twice and running syntax-check twice

In the distros using RPMs, we build libvirt once as a side effect
of running "ninja dist", and once via rpmbuild.

In addition "ninja dist" will run all tests including the "syntax-check"
suite, despite use having a separate "codestyle" job for for that.

There is no way to pass "--no-suite" when creating the dist, but if we
switch to invoking "meson dist", we can skip the build+test part
entirely  using "--no-tests".

When doing this we then run explicit "meson compile" and "meson test"
commands for the distros that don't build the RPMs, and in the latter
case we can now skip the "syntax-check" suite.

The RPM builds already skipped the "syntax-check" suite.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>