[Bug c++/51577] dependent name lookup finds operator in global namespace

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51577

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And the testcase from PR 61161:

struct T {
  template<typename T> void f(const T &v) {
    0 << v;
  }
};

namespace N {
  struct X {};
  struct Y : X {};
  void operator<<(int, const X&) {}
}

void operator<<(int, const N::Y&) = delete;

int main() {
  N::Y d;
  T().f(d);
}