[clang] [Clang][NFC] Add test for CWG2285 "Issues with structured bindings" (PR #126421)

[Yanzuo Liu via cfe-commits]

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@@ -196,6 +196,16 @@ void g() {
 #endif
 } // namespace cwg2277
 
+namespace cwg2285 { // cwg2285: 4
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zwuis wrote:

> It seems that Clang 5 was the first release which exhibits the correct behavior: https://godbolt.org/z/qabGrdvPq

`-std=c++1z` set `__cplusplus` to `201406L` in Clang 4. It was changed to `201703L` in https://github.com/llvm/llvm-project/commit/4b0cad0bb8731409c181f9a2cc9d266bb08321f9 (Clang 5). We need to remove the `#if` condition to test corresponding behaviour in Clang 4.

Do I need to add this note in test file?

https://github.com/llvm/llvm-project/pull/126421