Wayland Weston blank screen with drm-backend

[John Frankish]

> > > Using mesa-18.0.0, Wayland-1.14 and Weston 3.0.0 I get a blank 
> > > screen on a machine with intel hd4400 graphics when staring with:
> > >
> > > WAYLAND_DEBUG=1 EGL_LOG_LEVEL=debug XDG_RUNTIME_DIR=/run/user/$(id 
> > > -u) weston-launch >weston.log 2>&1
> > > 
> > > X works fine and, a couple of mesa upgrades ago, Weston worked fine 
> > > - full output log attached, any troubleshooting suggestions would be appreciated.
> > > 
> > Ah - it seems it is due to using "--with-cairo=glesv2" rather than "--with-cairo=image", but why?
> > 
> the glesv2 option has been discouraged for years, so no-one tests it.
> It's no surprise it's broken. You can see configure.ac warning you about it since May 2015.
> 
> It only exists so that one could theoretically build the couple demo programs that actually need it. > It's been a wish to rewrite those demos to not need it, since the demos themselves are
> still valuable, but no-one has had the time for it. That's also why the option has not been
> completely removed yet.
> 
Thanks for the explanation :)