[llvm-branch-commits] [clang] [HLSL] Define the HLSLRootSignature Attr (PR #123985)

[Finn Plummer via llvm-branch-commits]

inbelic wrote:

> I was expectng a change in `CGHLSLRuntime.cpp` that did something with the root signature attribute. Is there a reason why we aren't? That seems to be the pattern for other prs like this for `WaveSizeAttr` and `HLSLNumThreadsAttr`.

Yep, we will be using that to emit the metadata, which is addressed [here](https://github.com/llvm/llvm-project/pull/125131). I will get a reviewable version of that pr up soon.

This change just handles the construction of the attribute.

https://github.com/llvm/llvm-project/pull/123985