[clang] [llvm] [NFC][HLSL][DirectX] Let `HLSLRootSignature` reuse the `dxbc` defined enums (PR #145986)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `amdgpu-offload-rhel-8-cmake-build-only` running on `rocm-docker-rhel-8` while building `clang,llvm` at step 2 "update-annotated-scripts".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/204/builds/14340

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 2 (update-annotated-scripts) failure: update (failure)
git version 2.43.5
fatal: unable to access 'https://github.com/llvm/llvm-zorg.git/': Could not resolve host: github.com
fatal: unable to access 'https://github.com/llvm/llvm-zorg.git/': Could not resolve host: github.com

```

</details>

https://github.com/llvm/llvm-project/pull/145986