Fix DenseSet::ConstIterator typedefs

[bmoody]

Summary

Fix DenseSet::ConstIterator pointer/reference typedefs to be const

[dblaikie]

Thanks for the fix! (optionally, could put some static_asserts in the DenseSet unit test to validate that these changes have been made (is_const<...> etc)

[bmoody]

I don't have commit access, you're welcome to commit on my behalf. Thanks!

include/llvm/ADT/DenseSet.h

public:
   class ConstIterator {
     typename MapTy::const_iterator I;
     friend class DenseSet;
     friend class Iterator;
 
   public:
     using difference_type = typename MapTy::const_iterator::difference_type;
     using value_type = ValueT;
-    using pointer = value_type *;
-    using reference = value_type &;
+    using pointer = const value_type *;
+    using reference = const value_type &;
     using iterator_category = std::forward_iterator_tag;
 
     ConstIterator() = default;
     ConstIterator(const Iterator &B) : I(B.I) {}
     ConstIterator(const typename MapTy::const_iterator &i) : I(i) {}
 
     const ValueT &operator*() const { return I->getFirst(); }
     const ValueT *operator->() const { return &I->getFirst(); }