[clang] Add tests for CWG issues 6, 212, 232, 2823. (PR #165633)

[Richard Smith via cfe-commits]

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@@ -230,6 +230,37 @@ namespace cwg211 { // cwg211: 2.7
   };
 } // namespace cwg211
 
+namespace cwg212 { // cwg212: yes
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zygoloid wrote:

The value "yes" historically meant "there was never a time when we implemented any other behavior", which is the case here. Has this changed to mean just "we don't know when we started supporting this" instead? (I don't think that's an improvement: saying "2.7" here suggests that version 2.6 did something else, and a change was made in 2.7 to fix this, which isn't really true. But if that's what we're doing now, I guess it makes sense to be consistent with that.)

https://github.com/llvm/llvm-project/pull/165633