This MR exactly what it says on the tin - adds glamor support for Xvfb.
In the process of doing so, it removes the xf86 specifics from glamor_egl (glamor_xv still needs work). Then using it for Xvfb, while making possible Xwayland to drop it's glamor_egl-like implementation. But that for another day.
Current MR works like a charm with glxinfo, glxgears, waffle and apitrace.
Some nitpicks for later series:
DRM_IOCTL_I915_GEM_CONTEXT_DESTROY failed: Bad file descriptor