[clang] [CIR] Upstream Re-Throw with no return (PR #154994)

[Andy Kaylor via cfe-commits]

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@@ -657,6 +657,11 @@ class ScalarExprEmitter : public StmtVisitor<ScalarExprEmitter, mlir::Value> {
     return cgf.emitCXXNewExpr(e);
   }
 
+  mlir::Value VisitCXXThrowExpr(const CXXThrowExpr *e) {
+    cgf.emitCXXThrowExpr(e);
+    return nullptr;
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andykaylor wrote:

```suggestion
    return {};
```

https://github.com/llvm/llvm-project/pull/154994