[clang] Consider aggregate bases when checking if an InitListExpr is constant (PR #80519)

[Aaron Ballman via cfe-commits]

================
@@ -3328,6 +3328,12 @@ bool Expr::isConstantInitializer(ASTContext &Ctx, bool IsForRef,
            DIUE->getUpdater()->isConstantInitializer(Ctx, false, Culprit);
   }
   case InitListExprClass: {
+    // C++ [temp.dep.expr]p2:
----------------
AaronBallman wrote:

```suggestion
    // C++ [dcl.init.aggr]p2:
```
right?

https://github.com/llvm/llvm-project/pull/80519