[HLSL][DirectX] Compile a runnable shader from clang

[damyanp]

This is a milestone on the way to getting full HLSL support in Clang.

For this milestone we need to be able to compile a simple compute shader such that the resulting DXBC container can pass validation and be signed by the DXC validator and can therefore be executed on a non-developer mode Windows desktop PC. The shader compiler binary should come from some kind of nightly build, rather than building locally.

Sample shader

RWBuffer<int> In;
RWBuffer<int> Out;

[numthreads(8,1,1)]
void main(uint GI : SV_GroupIndex) {
  Out[GI] = In[GI] * In[GI];
}

Work

The work items listed here are expected to be fully completed - even if that means doing more than the bare minimum required to pass this milestone.

• [HLSL] Document HLSL resource IR representation and lowering #68006 (resources)
• [HLSL] Support RWBuffer loads and stores #91405
• [DXIL] generate dx.version metadata #88774 (dx.version metadata)
• [DirectX backend] generate ISG1, OSG1 parts for DXContainer #88778
• Build a demo app that executes this shader
• [HLSL] Set up internal nightly build that stores artifacts #90874
• [DirectX] Fix DXIL part header version encoding #89952
• [DirectX][DXIL] Set DXIL Version in DXIL target triple based on shader model version #90809