When we encounter a dependent type that was parsed before we know that

When we encounter a dependent type that was parsed before we know that
we were going to enter into the scope of a class template or class
template partial specialization, rebuild that type so that it can
refer to members of the current instantiation, as in code like

  template<typename T>
  struct X {
    typedef T* pointer;
    pointer data();
  };

  template<typename T>
  typename X<T>::pointer X<T>::data() { ... }

Without rebuilding the return type of this out-of-line definition, the
canonical return type of the out-of-line definition (a TypenameType)
will not match the canonical return type of the declaration (the
canonical type of T*).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@78316 91177308-0d34-0410-b5e6-96231b3b80d8