This commit adds support for the LunarG GLSL back-door as well as detecting
regular GLSL and SPIR-V. The SPIR-V path doesn't exist yet, so that will
cause an assert-fail.
This changes the way descriptor sets and layouts work so that we fill
out binding table contents at the time we bind descriptor sets. We
manipulate the binding table contents and sampler state in a shadow-copy
in anv_cmd_buffer. At draw time, we allocate the actual binding table
and sampler state and flush the anv_cmd_buffer copies.
This is by no means a complete solution to the binding table problems.
However, it does make texturing actually work. Before, we were texturing
from the render target since they were both starting at 0.
