[clang] [clang] Add tests for some CWG 5xx issues (PR #87909)

[Aaron Ballman via cfe-commits]

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@@ -661,6 +680,10 @@ namespace dr553 {
 }
 
 // dr554: na
+
+// dr555: na
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AaronBallman wrote:

https://cplusplus.github.io/CWG/issues/555.html is not a duplicate, it's marked CD5 not dup?

https://github.com/llvm/llvm-project/pull/87909