[milestone] 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 : register(u0);
RWBuffer<int> Out : register(u1);

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

Workstreams

Language (#21)

• numthreads entry attribute
• Entry function linkage rules

Resource Binding (#23)

• Explicit resource binding for UAVs #34
• Document resource binding annotations in language spec #55
• [HLSL] Collect explicit resource binding information llvm-project#110719

Semantics (#25)

• Support SV_GroupIndex and SV_DispatchThreadID used with basic scalar/vector input types for target shader.

Resources (#8)

• [DirectX] DXIL "typed" resource handles and buffer operations llvm-project#101555
• [HLSL] Frontend handling of "typed" resource types and buffer operations llvm-project#101557
• [HLSL] Eliminate resource global variables from module llvm-project#104271

DirectX Container (#9)

• [DirectX] generate resource table for PSV0 part llvm-project#103275