xwayland: Add preferred GLVND vendor to xwl_screen

If Xwayland's EGLstream backend supports hardware acceleration with the
NVIDIA closed-source driver, the GLX library also needs to be one
shipped by NVIDIA, that's what GLVND is for.

Add a new member to the xwl_screen that the backend can optionally set
to the preferred GLVND vendor to use.

If not set, "mesa" is assumed.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
(cherry picked from commit 24fc8aea1e)

hw/xwayland/xwayland-glx.c

@@ -378,6 +378,9 @@ egl_screen_probe(ScreenPtr pScreen)
         return NULL;
     }
 
+    if (!screen->base.glvnd && xwl_screen->glvnd_vendor)
+        screen->base.glvnd = strdup(xwl_screen->glvnd_vendor);
+
     if (!screen->base.glvnd)
         screen->base.glvnd = strdup("mesa");
 

hw/xwayland/xwayland-screen.h

@@ -107,6 +107,9 @@ struct xwl_screen {
     struct glamor_context *glamor_ctx;
 
     Atom allow_commits_prop;
+
+    /* The preferred GLVND vendor. If NULL, "mesa" is assumed. */
+    const char *glvnd_vendor;
 };
 
 /* Apps which use randr/vidmode to change the mode when going fullscreen,