PR libstdc++/69005
PR libstdc++/69222
* include/std/functional (function::_Invoke): Remove, use result_of.
(function::_Callable): Replace alias template with class template
and use partial specialization instead of _NotSelf alias template.
(function(_Functor)): Add "not self" constraint so that _Callable is
not used while type is incomplete.
* testsuite/20_util/function/69222.cc: New.
From-SVN: r232273