The main bulk of this is the new start screen code. To make this work in Raze some more work on the startup procedure is needed.
What this does provide is support for the DOS end-of-game text screens in Duke and SW on non-Windows systems.
* Serves no purpose in Raze or GZDoom and appears to only have been added to the backend to facilitate the older interpolation code that was excised in 893686709b.