mesa/st: Lower user clip planes for tess eval too
One new patch from !14399 (merged) that's in common code. Now that the d3d12 driver claims compat GLSL 400 (since ARB_gpu_shader5
is supported), a couple new tests lit up for using tessellation shaders with compat contexts, and gl_ClipVertex
coming out of TES was broken.
The logic in st_atom_shader.c leads me to believe this was supposed to work, but was incomplete to actually finish it.