[lldb] Fix deprecation warning for using std::iterator

[thakis]

Summary

std::iterator was deprecated in C++17.

No behavior change.

lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp

 //===-- DWARFDIE.cpp ------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "DWARFDIE.h"
 
 #include "DWARFASTParser.h"
 #include "DWARFDebugInfo.h"
 #include "DWARFDebugInfoEntry.h"
 #include "DWARFDeclContext.h"
 #include "DWARFUnit.h"
 
+#include "llvm/ADT/iterator.h"
+
 using namespace lldb_private;
 using namespace lldb_private::dwarf;
 
 namespace {
 
 /// Iterate through all DIEs elaborating (i.e. reachable by a chain of
 /// DW_AT_specification and DW_AT_abstract_origin attributes) a given DIE. For
 /// convenience, the starting die is included in the sequence as the first
 /// item.
 class ElaboratingDIEIterator
-    : public std::iterator<std::input_iterator_tag, DWARFDIE> {
+    : public llvm::iterator_facade_base<
+          ElaboratingDIEIterator, std::input_iterator_tag, DWARFDIE,
+          std::ptrdiff_t, DWARFDIE *, DWARFDIE *> {
 
   // The operating invariant is: top of m_worklist contains the "current" item
   // and the rest of the list are items yet to be visited. An empty worklist
   // means we've reached the end.
   // Infinite recursion is prevented by maintaining a list of seen DIEs.
   // Container sizes are optimized for the case of following DW_AT_specification
   // and DW_AT_abstract_origin just once.
   llvm::SmallVector<DWARFDIE, 2> m_worklist;
public:
   /// End marker
   ElaboratingDIEIterator() = default;
 
   const DWARFDIE &operator*() const { return m_worklist.back(); }
   ElaboratingDIEIterator &operator++() {
     Next();
     return *this;
   }
-  ElaboratingDIEIterator operator++(int) {
-    ElaboratingDIEIterator I = *this;
-    Next();
-    return I;
-  }
 
   friend bool operator==(const ElaboratingDIEIterator &a,
                          const ElaboratingDIEIterator &b) {
     if (a.m_worklist.empty() || b.m_worklist.empty())
       return a.m_worklist.empty() == b.m_worklist.empty();
     return a.m_worklist.back() == b.m_worklist.back();
   }
-  friend bool operator!=(const ElaboratingDIEIterator &a,
-                         const ElaboratingDIEIterator &b) {
-    return !(a == b);
-  }
 };
 
 llvm::iterator_range<ElaboratingDIEIterator>
 elaborating_dies(const DWARFDIE &die) {
   return llvm::make_range(ElaboratingDIEIterator(die),
                           ElaboratingDIEIterator());
 }
 } // namespace