Fix ABI break I made in r203587; thanks to Richard Smith for the catch.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@203610 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/iterator b/include/iterator
index 4c6b0a6..263ff3f 100644
--- a/include/iterator
+++ b/include/iterator
@@ -538,16 +538,18 @@
 {
 protected:
     _Iter current;
+private:
+    mutable _Iter __t;  // no longer used as of LWG #2360, not removed due to ABI break
 public:
     typedef _Iter                                            iterator_type;
     typedef typename iterator_traits<_Iter>::difference_type difference_type;
     typedef typename iterator_traits<_Iter>::reference       reference;
     typedef typename iterator_traits<_Iter>::pointer         pointer;
 
-    _LIBCPP_INLINE_VISIBILITY reverse_iterator() : current() {}
-    _LIBCPP_INLINE_VISIBILITY explicit reverse_iterator(_Iter __x) : current(__x) {}
+    _LIBCPP_INLINE_VISIBILITY reverse_iterator() : current(), __t() {}
+    _LIBCPP_INLINE_VISIBILITY explicit reverse_iterator(_Iter __x) : current(__x), __t() {}
     template <class _Up> _LIBCPP_INLINE_VISIBILITY reverse_iterator(const reverse_iterator<_Up>& __u)
-        : current(__u.base()) {}
+        : current(__u.base()), __t() {}
     _LIBCPP_INLINE_VISIBILITY _Iter base() const {return current;}
     _LIBCPP_INLINE_VISIBILITY reference operator*() const {_Iter __tmp = current; return *--__tmp;}
     _LIBCPP_INLINE_VISIBILITY pointer  operator->() const {return _VSTD::addressof(operator*());}