[Bug c++/91418] Nested class of templated class cannot declare parent class friend

[harald at gigawatt dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91418

--- Comment #3 from Harald van Dijk <harald at gigawatt dot nl> ---
I believe GCC is correct here. [class.friend]p11
(http://eel.is/c++draft/class.friend#11) specifies that `friend class A;`, with
an unqualified name, does not find the global scope class A, but makes a (never
defined) local class A a friend of B. An example that actually defines it shows
how this could be used:

  class A {
  public:
    void func() {
      class B {
        B() = default;
        friend class A;
      };
      class A {
      public:
        A() { B(); }
      };
      A();
    }
  };