Per operator: don't forget Intel + virgl, and prepare for future NVIDIA. Intel
(iris/anvil) and virgl need NO LLVM GPU backend (NIR / virtualized) — they stay
in Mesa's driver lists as first-class targets. AMD needs AMDGPU (now); NVIDIA
(future, nouveau/NVK) needs NVPTX. LLVM rebuilds are very expensive, so include
NVPTX now (llvm21: X86;AMDGPU;NVPTX) to avoid an LLVM rebuild when NVIDIA lands.
Documented the vendor->driver->LLVM-backend matrix in the amd64-only policy.
vasilito
ce8359342c