Bug 1606941 - prefer GLX in glxtest for now r=stransky

WebRender qualification needs actual GPU vendor info.
It's currently only available through GLX
(eglQueryRendererIntegerMESA is not available yet)
so let's only use the Wayland native path for non-Xwayland systems for now.

Differential Revision: https://phabricator.services.mozilla.com/D58656

--HG--
extra : moz-landing-system : lando

toolkit/xre/glxtest.cpp

@@ -552,8 +552,9 @@ bool fire_glxtest_process() {
     write_end_of_the_pipe = pfd[1];
     close_logging();
     // TODO: --display command line argument is not properly handled
+    // NOTE: prefers X for now because eglQueryRendererIntegerMESA does not exist yet
 #ifdef MOZ_WAYLAND
-    if (IsWaylandDisabled() || !wayland_egltest())
+    if (IsWaylandDisabled() || getenv("DISPLAY") || !wayland_egltest())
 #endif
       glxtest();
     close(pfd[1]);