Based on tests, skips triangles with any point outside the 4096x4096 box,
except when depth clamping would engage.

Also D3D11, since they are very similar.

Vulkan clamps to the clip range, not the full range.  So when clipping, we
don't really want to clamp at all.  Unfortunately, when one side is
clipping, we can't do it exactly right.

But many games clip depth, like Dissidia.  Fixes hrydgard#11260.