ci: run piglit on d3d12 driver
This MR implements GitLab CI support for running Piglit on the D3D12 driver.
There's a few of things to note:
- The tests are run on WARP, Microsoft's high-performance D3D12 software rasterizer. This is a Windows component, and the version we're using is unfortunately a bit buggy, so there's a lot of extra failures caused by this. Sadly, upgrading this is easier said than done. I'm sure @daniels will bother explaining why to anyone who really wants the full story ;)
- In order to add support for testing for instance LLVMpipe on Windows, there's a bit more work needed, to supply the script with different expected test-results. I think that could be left for whenever someone bothers to wire up LLVMpipe.
So, with this, I think the D3D12 driver is at a place where future releases can be cut from upstream instead of our downstream branch!