This pr relands https://github.com/llvm/llvm-project/pull/133302.
It resolves two issues:
- Linking error during build,
[here](https://github.com/llvm/llvm-project/pull/133302#issuecomment-2767259848).
There was a missing dependency for `clangLex` for the
`ParseHLSLRootSignatureTest.cpp` unit testing. This library was added to
the dependencies to resolve the error. It wasn't caught previously as
the library was transitively linked in most build environments
- Warning of unused declaration,
[here](https://github.com/llvm/llvm-project/pull/133302#issuecomment-2767091368).
There was a usability line in `LexHLSLRootSignature.h` of the form
`using TokenKind = enum RootSignatureToken::Kind` which causes this
error. The declaration is removed from the header file to be used
locally in the `.cpp` files that use it.
Notably, the original pr would also exposed `clang::hlsl::TokenKind` to
everywhere it was included, which had a name clash with
`tok::TokenKind`. This is another motivation to change to the proposed
resolution.
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Co-authored-by: Finn Plummer <finnplummer@microsoft.com>
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