[clang] [clang] Improve diagnostic on [[nodiscard]] attribute (PR #112521)

[via cfe-commits]

================
@@ -290,9 +296,10 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S, unsigned DiagID) {
     if (E->getType()->isVoidType())
       return;
 
-    if (DiagnoseNoDiscard(*this, cast_or_null<WarnUnusedResultAttr>(
-                                     CE->getUnusedResultAttr(Context)),
-                          Loc, R1, R2, /*isCtor=*/false))
+    const auto &[OffendingDecl, A] = CE->getUnusedResultAttr(Context);
----------------
Sirraide wrote:

```suggestion
    auto [OffendingDecl, A] = CE->getUnusedResultAttr(Context);
```

https://github.com/llvm/llvm-project/pull/112521