[AsmParser] Use a range-based for loop (NFC) (#168488)

Identified with modernize-loop-convert.

Author: kazutakahirata

llvm/lib/AsmParser/LLParser.cpp

@@ -315,11 +315,10 @@ bool LLParser::validateEndOfModule(bool UpgradeDebugInfo) {
       return error(NT.second.second,
                    "use of undefined type '%" + Twine(NT.first) + "'");
 
-  for (StringMap<std::pair<Type*, LocTy> >::iterator I =
-       NamedTypes.begin(), E = NamedTypes.end(); I != E; ++I)
-    if (I->second.second.isValid())
-      return error(I->second.second,
-                   "use of undefined type named '" + I->getKey() + "'");
+  for (const auto &[Name, TypeInfo] : NamedTypes)
+    if (TypeInfo.second.isValid())
+      return error(TypeInfo.second,
+                   "use of undefined type named '" + Name + "'");
 
   if (!ForwardRefComdats.empty())
     return error(ForwardRefComdats.begin()->second,