Gallium: add lowering of depth clamp for drivers that don't support it and enable it for virgl
This series implements lowering of depth clamp in TGSI to provide ARB_depth_clamp/EXT_depth_clamp on hardware that doesn't support it. Most of the lowering code was implemented by @kusma and I've added support for GS and TES shaders and the interaction with ARB_clip_control.
Additional piglits to verify this code are provided by piglit!99
Edited by Gert Wollny