[Driver] Avoid repeated map lookups (NFC) (#122625)

Author: kazutakahirata

clang/lib/Driver/Driver.cpp

@@ -2534,8 +2534,8 @@ enum {
 static unsigned PrintActions1(const Compilation &C, Action *A,
                               std::map<Action *, unsigned> &Ids,
                               Twine Indent = {}, int Kind = TopLevelAction) {
-  if (Ids.count(A)) // A was already visited.
-    return Ids[A];
+  if (auto It = Ids.find(A); It != Ids.end()) // A was already visited.
+    return It->second;
 
   std::string str;
   llvm::raw_string_ostream os(str);