Maybe I spent too much time with *BSD's (and Linux), but I don't see "rock solid ABI" as that useful. If I wanted to make a program that'd still be usable in 50 years, I'd provide source code, in C with minimal dependencies. Sure, the build system is likely to rot, but every modern C compiler supports C89, a 35 year old standard. Just don't go overboard with something like Qt or GTK. And yes, I'll have to constrain myself to not use nice modern libraries.. but those constrains would be much more permissive than all-new isolated "uxtal" VM.

(For the specific application of games / graphics, I'd go with libSDL. Version 1.0 was released in 1998, and my current machine still has "libsdl1.2-compat" installable and supported. But I don't play games much so I know much less about those.)