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

[Vlad Serebrennikov via cfe-commits]

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@@ -90,6 +90,24 @@ namespace cwg5 { // cwg5: 3.1
   const C c = e;
 } // namespace cwg5
 
+namespace cwg6 { // cwg6 codegen is tested in cwg6.cpp
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Endilll wrote:

Can you move non-codegen part of the test to `cwg6.cpp`? It's unfortunate to split them like this. See `cwg2353.cpp` for an example.

Don't forget to leave `// cwg6 is in cwg6.cpp` here

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