This is now separated in two patches: * 1/2 add the constructor and assigment for any other tuple-like type, with zero elements (only array<T, 0> currently) * 2/2 implements const-qualified copy-assigment for tuple<>, in a way to does not make tuple non-trivially copyable
Tested on x86_64-linux locally. All *tuple* test tested in all supported modes. Double checked this time if new test are marked as passed when they are expected to.
