[clang] [clang] Add diagnostic for friend declaration of closure type member (PR #191419)

[Corentin Jabot via cfe-commits]

================
@@ -222,3 +222,19 @@ template <template <typename> class Template, typename Argument>
 using Bind = Instantiate<Internal<Template>::template Bind, Argument>;
 #endif
 } // namespace cwg1794
+
+namespace cwg1780 { // cwg1780: 22
----------------
cor3ntin wrote:

```suggestion
namespace cwg1780 { // cwg1780: 23
```

https://github.com/llvm/llvm-project/pull/191419