[clang] [Clang] Introduce OverflowBehaviorType for fine-grained overflow control (PR #148914)

[Matheus Izvekov via cfe-commits]

================
@@ -405,6 +405,10 @@ ArgType::matchesType(ASTContext &C, QualType argTy) const {
     argTy = PT->getPointeeType();
   }
 
+  if (const OverflowBehaviorType *OBT =
+          dyn_cast<OverflowBehaviorType>(argTy.getCanonicalType()))
+    argTy = OBT->getUnderlyingType();
+
----------------
mizvekov wrote:

Should this really canonicalize? It seems to me if the udnerlying type has a typedef that is meaningful here, we would still want to use that information here, right?
```suggestion
  if (const auto *OBT = argTy->getAs<OverflowBehaviorType>())
    argTy = OBT->getUnderlyingType();
```

https://github.com/llvm/llvm-project/pull/148914