[NFC] Add iterator traits to BitVector set_bits_iterator

llvm/include/llvm/ADT/BitVector.h

 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/MathExtras.h"
 #include <algorithm>
 #include <cassert>
 #include <climits>
 #include <cstdint>
 #include <cstdlib>
 #include <cstring>
+#include <iterator>
 #include <utility>
 
 namespace llvm {
 
 /// ForwardIterator for the bits that are set.
 /// Iterators get invalidated when resize / reserve is called.
 template <typename BitVectorT> class const_set_bits_iterator_impl {
   const BitVectorT &Parent;
   int Current = 0;
 
   void advance() {
     assert(Current != -1 && "Trying to advance past end.");
     Current = Parent.find_next(Current);
   }
 
 public:
+  using iterator_category = std::forward_iterator_tag;
+  using difference_type   = void;
+  using value_type        = int;
+  using pointer           = value_type*;
+  using reference         = value_type&;
+
   const_set_bits_iterator_impl(const BitVectorT &Parent, int Current)
       : Parent(Parent), Current(Current) {}
   explicit const_set_bits_iterator_impl(const BitVectorT &Parent)
       : const_set_bits_iterator_impl(Parent, Parent.find_first()) {}
   const_set_bits_iterator_impl(const const_set_bits_iterator_impl &) = default;
 
   const_set_bits_iterator_impl operator++(int) {
     auto Prev = *this;