Flycast core does not render properly.

[JSensebe]

The flycast_libretro core, whether running Naomi or Dreamcast software, does not render correctly, similar to the issue with Vectrex rendering. It is using ModernGlVideoDriver. No errors are given, but the core issues the following warning:

Warning (from warnings module):
  File "C:\Users\jsens\AppData\Roaming\Python\Python312\site-packages\libretro\drivers\video\opengl\moderngl.py", line 674
    warnings.warn(
UserWarning: Core requested stencil attachment, but moderngl lacks support; ignoring

[JesseTG]

Ah, damn. I guess I'll need to either contribute stencil buffer support to moderngl or switch to another OpenGL package -- that depends on what my options are for supporting OpenGL ES and legacy OpenGL contexts.