[llvm] Fix build failure in DXILResource.h on newer versions of MSVC (PR #139309)

[Daniel Paoliello via llvm-commits]

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@@ -670,6 +670,8 @@ class DXILResourceBindingInfo {
       return CBufferSpaces;
     case dxil::ResourceClass::Sampler:
       return SamplerSpaces;
+    default:
+      llvm_unreachable("Invalid resource class");
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dpaoliello wrote:

Good call.

https://github.com/llvm/llvm-project/pull/139309