[clang] Disallow btf_type_tag in C++ mode (PR #107238)

[Erich Keane via cfe-commits]

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@@ -6490,6 +6490,15 @@ static void HandleBTFTypeTagAttribute(QualType &Type, const ParsedAttr &Attr,
                                       TypeProcessingState &State) {
   Sema &S = State.getSema();
 
+  // This attribute is only supported in C.
+  // FIXME: we should implement checkCommonAttributeFeatures() in SemaAttr.cpp
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erichkeane wrote:

OOof weird.... Yeah, an issue to make it clear whether they really want `DeclOrType` is probably the right way.  If you could find whoever should own that issue and assign it, it would be appreciated.

https://github.com/llvm/llvm-project/pull/107238