XCB/X11: disable ARGB support

VLC does not currently handle color masks for ARGB chromas, so this can
not work yet. Instead, fail safe to the GLX output.
(cherry picked from commit 2e2bf09f)

modules/video_output/xcb/x11.c

@@ -178,8 +178,13 @@ static int Open (vlc_object_t *obj)
           case 32:
             if (fmt->bits_per_pixel != 32)
                 continue;
+#ifdef FIXED_VLC_RGBA_MASK
             fmt_pic.i_chroma = VLC_CODEC_RGBA;
             break;
+#else
+            msg_Dbg (vd, "X11 visual with alpha-channel not supported");
+            continue;
+#endif
           case 24:
             if (fmt->bits_per_pixel == 32)
                 fmt_pic.i_chroma = VLC_CODEC_RGB32;