[clang] [Clang] Implement P0963R3 "Structured binding declaration as a condition" (PR #130228)

[via cfe-commits]

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@@ -5189,6 +5197,12 @@ template <class Emitter> bool Compiler<Emitter>::visitIfStmt(const IfStmt *IS) {
       return false;
   }
 
+  if (auto *DD =
+          dyn_cast_if_present<DecompositionDecl>(IS->getConditionVariable());
+      DD && DD->isDecisionVariable())
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cor3ntin wrote:

When is `DD->isDecisionVariable()` false? Should we assert instead?
Ditto elsewhere

https://github.com/llvm/llvm-project/pull/130228