Meta: Use non-VGA VirtIO GPU variants when running on macOS

It appears that QEMU on macOS doesn't have the VirtIO GPU variants that
support VGA functionality. Those variants are not especially important
to us, because we don't use any kind of VGA functionality in our kernel
anyway.

Therefore, for macOS, we could decide to use virtio-gpu-gl-pci and
virtio-gpu-pci devices instead.

Meta/run.sh

@@ -200,12 +200,26 @@ fi
 SERENITY_GL="${SERENITY_GL:-0}"
 if [ -z "$SERENITY_QEMU_DISPLAY_DEVICE" ]; then
     if [ "$SERENITY_GL" = "1" ]; then
-        SERENITY_QEMU_DISPLAY_DEVICE="virtio-vga-gl "
+        # QEMU appears to not support the GL backend for VirtIO GPU variant on macOS.
+        if [ "$(uname)" = "Darwin" ]; then
+            die "SERENITY_GL is not supported since there's no GL backend on macOS"
+        else
+            SERENITY_QEMU_DISPLAY_DEVICE="virtio-vga-gl "
+        fi
+        
         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=$SERENITY_SCREENS "
+        # QEMU appears to not support the virtio-vga VirtIO GPU variant on macOS.
+        # To ensure we can still boot on macOS with VirtIO GPU, use the virtio-gpu-pci
+        # variant, which lacks any VGA compatibility (which is not relevant for us anyway).
+        if [ "$(uname)" = "Darwin" ]; then
+            SERENITY_QEMU_DISPLAY_DEVICE="virtio-gpu-pci,max_outputs=$SERENITY_SCREENS "
+        else
+            SERENITY_QEMU_DISPLAY_DEVICE="virtio-vga,max_outputs=$SERENITY_SCREENS "
+        fi
+
         # 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
         # displays force using relative coordinates only