Build and xwayland issue with GL/EGL dependencies, thus building of xorg fails

There unfortunately is a rather messy situation when trying to build Xorg on Arch currently. I built libglvnd to include headers by commenting out --disable-headers. I installed it as a dependency for mesa git-master. mesa git-master correctly builds and installs. Now, when I try to build xorg git-master, it fails: glamorerror.log

When I downgrade to stable Arch repository versions of mesa and libglvnd, I can successfully build xorg git-master again. However: XWayland programs like Firefox/Chromium can't establish a GL context and thus silently fall back to software rendering. For whatever reason, no error log entries show up when running glxgears on xwayland. Does it silently fall back to llvmpipe? GLX/EGL contexts on native xorg seem to work without issues though.

I don't know if mesa is actually to blame for these issues. However, I'm a bit worried about (packaging) issues for the 19.2.2 release. So it shouldn't hurt to mention it here.

There is also this report on the xserver bugtracker: xorg/xserver#914 (closed)