[llvm-xray] Use llvm::make_second_range (NFC) (#135989)

Author: kazutakahirata

Diff for: llvm/tools/llvm-xray/xray-stacks.cpp

@@ -495,15 +495,8 @@ class StackTrie {
   void printIgnoringThreads(raw_ostream &OS, FuncIdConversionHelper &FN) {
     RootVector RootValues;
 
-    // Function to pull the values out of a map iterator.
-    using RootsType = decltype(Roots.begin())::value_type;
-    auto MapValueFn = [](const RootsType &Value) { return Value.second; };
-
-    for (const auto &RootNodeRange :
-         make_range(map_iterator(Roots.begin(), MapValueFn),
-                    map_iterator(Roots.end(), MapValueFn))) {
+    for (const auto &RootNodeRange : make_second_range(Roots))
       llvm::append_range(RootValues, RootNodeRange);
-    }
 
     print(OS, FN, RootValues);
   }