radeonsi: zero init variable by default
This MR tries to resolve rendering bugs caused by uninitialized variables in a way the doesn't penalize correct applications.
It solves the problem for at least the following apps/shadertoy:
- #2689 (closed)
- #2598 (closed)
shader-db results summary is (updated for v2):
|All affected||6.5%||-0.10%||1.78 %||4.20 %||.||.||.||0.70 %||-0.04 %||.|
All affected shaders I've looked at have use-uninitialized-variable kind of bugs.