This code compiles on gcc but not on clang. Which compiler is correct, and how to make it compile on clang-14, without modifying A‘s code?

Using clang v14.0.0 on Ubuntu 22.04.
It works on the latest unstable version on clang, not available in apt repos, and I would like to fix this code without having to install manually the toolchains just for this, since I expect not everybody will have the trunk version installed.

#include <iostream>
#include <cstdint>

template<typename T>
class B
{
};

class A
{
    struct Sub {
        int r;
    };

    template<typename>
    friend class B;
};

template<>
struct B<int>
{
    template<typename T>
    using Sub = typename T::Sub;
};

int main()
{
    int i = offsetof(B<int>::Sub<A>, r);
}

error from clang 14.0.0:

<source>:23:5: error: 'Sub' is a private member of 'A'
    using Sub = typename T::Sub;
    ^
<source>:11:12: note: implicitly declared private here
    struct Sub {
           ^