[Sema] Avoid repeated hash lookups (NFC) (llvm#111090)

Author: kazutakahirata

clang/lib/Sema/SemaLambda.cpp

@@ -423,11 +423,11 @@ bool Sema::DiagnoseInvalidExplicitObjectParameterInLambda(
   // is an empty cast path for the method stored in the context (signalling that
   // we've already diagnosed it) and then just not building the call, but that
   // doesn't really seem any simpler than diagnosing it at the call site...
-  if (auto It = Context.LambdaCastPaths.find(Method);
-      It != Context.LambdaCastPaths.end())
+  auto [It, Inserted] = Context.LambdaCastPaths.try_emplace(Method);
+  if (!Inserted)
     return It->second.empty();
 
-  CXXCastPath &Path = Context.LambdaCastPaths[Method];
+  CXXCastPath &Path = It->second;
   CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
                      /*DetectVirtual=*/false);
   if (!IsDerivedFrom(RD->getLocation(), ExplicitObjectParameterType, LambdaType,