[clang] [clang][AMDGPU] Clean-up handling of named barrier type (PR #207687)

[Matt Arsenault via cfe-commits]

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@@ -14263,6 +14263,17 @@ def note_acc_reduction_combiner_forming
     : Note<"while forming %select{|binary operator '%1'|conditional "
            "operator|final assignment operator}0">;
 
+// AMDGCN type diagnostics
+def err_amdgcn_invalid_field_not_a_wrapper : Error<
+  "%0 is only allowed as a field if the %select{struct|interface|union|class|enum}1"
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arsenm wrote:

I think trying to permit this is creating a convoluted edge case. I'd prefer to just go back to treating it as a standard opaque types with all the restrictions that entails rather than making this narrow exception 

https://github.com/llvm/llvm-project/pull/207687