Meta: Add SERENITY_GL environment variable to run.sh

Author: https://github.com/ccapitalK
Commit: https://github.com/SerenityOS/serenity/commit/04849c9561
Pull-request: https://github.com/SerenityOS/serenity/pull/12619
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/sunverwerth
Reviewed-by: https://github.com/supercomputer7

Meta/run.sh

@@ -187,8 +187,14 @@ else
     SERENITY_QEMU_DISPLAY_BACKEND="${SERENITY_QEMU_DISPLAY_BACKEND:-gtk,gl=off}"
 fi
 
+SERENITY_GL="${SERENITY_GL:-0}"
 if [ -z "$SERENITY_QEMU_DISPLAY_DEVICE" ]; then
-    if [ "$SERENITY_SCREENS" -gt 1 ]; then
+    if [ "$SERENITY_GL" = "1" ]; then
+        SERENITY_QEMU_DISPLAY_DEVICE="virtio-vga-gl "
+        if [ "$SERENITY_SCREENS" -gt 1 ]; then
+            die "SERENITY_GL and multi-monitor support cannot be setup simultaneously"
+        fi
+    elif [ "$SERENITY_SCREENS" -gt 1 ]; then
         SERENITY_QEMU_DISPLAY_DEVICE="virtio-vga,max_outputs=$SERENITY_SCREENS "
         # QEMU appears to always relay absolute mouse coordinates relative to the screen that the mouse is
         # pointed to, without any way for us to know what screen it was. So, when dealing with multiple