Cleanup: clarify license and origin of voronoi and dithering code

Cleanup: compiler warnings

Fix EGL version being printed on every startup

After the switch to enable EGL over GLX. No need to print this debugging
information always.

Render: disable Z pass by default, leave only Combined

It was somewhat arbitrary to have this one pass enabled that adds a bit of
additional memory and render time overhead, even though it's not necessarily
more important than others.

Render: remove unused Blender Internal view layer settings

These should have been removed earlier but were forgotten.

Fix T90295: inconsistent render pass order between Cycles and Eevee

Fix LLVM 12 symbol conflict with Mesa drivers, after recent Linux libs update

Cycles: remove WITH_CYCLES_DEBUG, add WITH_CYCLES_DEBUG_NAN

WITH_CYCLES_DEBUG was used for rendering BVH debugging passes. But since we
mainly use Embree an OptiX now, this information is no longer important.

WITH_CYCLES_DEBUG_NAN will enable additional checks for NaNs and invalid values
in the kernel, for Cycles developers. Previously these asserts where enabled in
all debug builds, but this is too likely to crash Blender in scenes that render
fine regardless of the NaNs. So this is behind a CMake option now.

Fixes T90240

Fix Python error in benchmark executable detection after recent changes

Cycles: upgrade CUDA to 11.4

This fixes a performance regression on Ampere cards, on specific scenes like
classroom. For cycles-x there is little difference, but this is still helpful
for LTS releases, and we need to upgrade at some point anyway.