[Bug c++/68093] [concepts] friend function declarations that differ only by constraints are rejected as redefinitions

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68093

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is the accepts-invalid example from PR 86978:

template <typename t>
struct S
{
    template <typename t2>
        requires false
    friend void foobar(S, t2) {}
};

int main()
{
    foobar(S<double>{}, int{});
}