[clang] [Clang] disallow # operators in attribute argument lists (PR #147308)

[Aaron Ballman via cfe-commits]

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@@ -678,6 +678,8 @@ Improvements to Clang's diagnostics
 - Clang now accepts ``@tparam`` comments on variable template partial
   specializations. (#GH144775)
 
+- Clang now rejects ``#`` operators in attribute argument lists. (#GH147217)
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AaronBallman wrote:

```suggestion
- Clang rejects the ``#`` and ``##`` preprocessor tokens in an attribute argument list in C++. The operators can be used in macro replacement lists with the usual preprocessor semantics. What is rejected are non-preprocessor uses of the tokens. The same restrictions do not apply in C. (#GH147217)
```
Will need to wrap to 80 columns

https://github.com/llvm/llvm-project/pull/147308