[clang] [HLSL][DirectX] Add the Qdx-rootsignature-strip driver option (PR #154454)

[Justin Bogner via cfe-commits]

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@@ -4647,6 +4647,16 @@ void Driver::BuildDefaultActions(Compilation &C, DerivedArgList &Args,
     // Only add action when needValidation.
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bogner wrote:

The comments around the isDXIL block look like they're out of date or at least misplaced (both this one and the "Call validator" one above.

https://github.com/llvm/llvm-project/pull/154454