arch linux: weston 5.0.0 not working with nouveau

[Dirk Eibach]

I did a git bisect and found the commit "244244d1 (refs/bisect/bad)
compositor-drm: Use GBM modifier API" introduced the problem.
Am Mo., 10. Sep. 2018 um 10:12 Uhr schrieb Dirk Eibach
<dirk.eibach at googlemail.com>:
>
> Perhaps I should add, that with rolling back to weston 4.0.0.
> everything works fine. So nouveau support must have been broken
> somewhere inbetween.
> Am Mo., 10. Sep. 2018 um 08:59 Uhr schrieb Dirk Eibach
> <dirk.eibach at googlemail.com>:
> >
> > > Looks like some drm issue. Just wondering if you can use KMS APIs directly without seeing this issue? So for example, will kmscube draw something on the screen (https://github.com/robclark/kmscube)? BTW, noticed that you are using /dev/dri/card1 in your logs. What's at card0? Note that this kmscube will only open a handle to card0 so you may want to change that and test.
> >
> > Removed the second graphics adapter. kmscube works fine.
> >
> > Cheers
> > Dirk