On X11 windowing systems there's no `MessageBox` prompt like on
win32 that could show users that they have unsupported GPUs,
this leads to confusion to them as they typically don't open
blender from a command line so none of the messages could be
available. This patch utilizes `system->showMessageBox` to display
a GUI message box telling the user that the GPU is unsupported.
Pull Request: https://projects.blender.org/blender/blender/pulls/126220
04c5a9f053