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

[Erich Keane via cfe-commits]

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@@ -225,6 +225,11 @@ Attribute Changes in Clang
   more cases where the returned reference outlives the object.
   (#GH100567)
 
+- Now correctly diagnosing use of ``btf_type_tag`` in C++ and ignoring it; this
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erichkeane wrote:

```suggestion
- Clang now correctly diagnoses the use of ``btf_type_tag`` in C++ and ignores it; this
```

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