[clang] [HLSL] Implement the dst HLSL Function (PR #133828)

[Ashley Coleman via cfe-commits]

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@@ -174,6 +174,31 @@ const inline float distance(__detail::HLSL_FIXED_VECTOR<float, N> X,
                             __detail::HLSL_FIXED_VECTOR<float, N> Y) {
   return __detail::distance_vec_impl(X, Y);
 }
+//===----------------------------------------------------------------------===//
+// dst builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn fvector dst( fvector, fvector)
+/// \brief Returns the length of a vector
+/// \param Src0 [in] The first vector contain {_, d*d, d*d, _}
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V-FEXrt wrote:

Similar idea here. I'm not sure that `contain {_, d*d, d*d, _}` isn't very helpful without context

https://github.com/llvm/llvm-project/pull/133828