I don't remember having anything useful besides some quick hacks and I don't
have them anymore. I came to the conclusion ARB_depth_clamp is not
implementable on r300-r500. I don't think the extended range [-2,2] would help
and IIRC, the register is not allowed to be written by userspace anyway, it
must be written in the kernel.

The way I see it, there are 4 solutions to this issue:

1) Wine shouldn't use ARB_depth_clamp, but instead it should use an extension
that exposes CLIP_DISABLE as defined by D3D9 to the user. The problem is such
an extension doesn't exist.

2) We could agree on a wine-specific hack for r300g, which would expose
ARB_depth_clamp for Wine only. We already blacklist certain apps for Hyper-Z,
this would be no different.

3) We could clamp POS.Z to the range [-POS.W, POS.W] in the vertex shader. The
problem with this approach is the clamping should be per-pixel, not per-vertex.

4) Disabling ARB_depth_clamp again.