[clang] [CUDA][HIP] Fix CTAD for host/device constructors (PR #168711)

[Corentin Jabot via cfe-commits]

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@@ -7984,6 +7984,19 @@ void Sema::ProcessDeclAttributeList(
     }
   }
 
+  // CUDA/HIP: disallow explicit CUDA target attributes on deduction guides.
+  // Deduction guides are not callable functions and never participate in
+  // codegen; they are always treated as host+device for CUDA/HIP semantic
+  // checks, so explicit target attributes on them would be misleading noise.
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cor3ntin wrote:

```suggestion
  // checks, so explicit target attributes on them would be misleading.
```

https://github.com/llvm/llvm-project/pull/168711