[clang] [libcxx] [Clang] Diagnose forming references to nullptr (PR #143667)

[Shafik Yaghmour via cfe-commits]

================
@@ -5242,7 +5281,10 @@ static bool EvaluateVarDecl(EvalInfo &Info, const VarDecl *VD) {
   if (InitE->isValueDependent())
     return false;
 
-  if (!EvaluateInPlace(Val, Info, Result, InitE)) {
+  if (VD->getType()->isReferenceType() &&
----------------
shafik wrote:

Can we a comment explaining this `if`?

https://github.com/llvm/llvm-project/pull/143667