[clang] [Clang] Treat constexpr-unknown value as invalid in `evaluateValue` (PR #128409)

[Eli Friedman via cfe-commits]

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@@ -122,9 +122,9 @@ namespace CaseStatements {
 }
 
 extern int &Recurse1;
-int &Recurse2 = Recurse1; // expected-note {{declared here}}
+int &Recurse2 = Recurse1; // pre-cxx23-note {{declared here}}
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efriedma-quic wrote:

I'd guess you just need to generate a note when you set `Result = false`, like `the value 'Recurse2' is constexpr-unknown`.

https://github.com/llvm/llvm-project/pull/128409