accepts-invalid with C++23 constexpr-unknown with struct containing reference

[efriedma-quic]

int &ff();
int &x = ff();
struct A { int& x; };
constexpr A g = {x};
const A* gg = &g;

Should be rejected, currently accepted. (And related variations miscompile.)

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Eli Friedman (efriedma-quic)

``` int &ff(); int &x = ff(); struct A { int& x; }; constexpr A g = {x}; const A* gg = &g; ```

Should be rejected, currently accepted. (And related variations miscompile.)

[frederick-vs-ja]

A simpler example (Godbolt link):

int &ff();
int &x = ff();
constexpr int &y = x;

[cor3ntin]

@shafik