After working around the bugs described in #93551 and getting the game running,
I noticed that unless the shadow quality setting was at "Ultra", all rendered
shadows are blocky and jagged, with gaps appearing between the shadows cast be
apparently solid objects.

I messed around with some driconf options, and discovered that this rendering
issue goes away if setting the "glsl_correct_derivatives_after_discard" option.

Unfortunately, I couldn't get a working apitrace because of the LD_PRELOAD
hacks, but attached are two screenshots of roughly the same area, one without
the option (before.png) and one with (after.png).