* include/std/functional (_Mu<A, false, true>, _Mu<A, true, false>):
	Simplify forwarding from tuple of references.
	(_Maybe_wrap_member_pointer): Remove.
	(_Bind::__call, _Bind::__call_c, _Bind::__call_v, _Bind::__call_c_v):
	Use std::__invoke.
	(_Bind::_Mu_type, _Bind::_Res_type_impl, _Bind::_Res_type)
	(_Bind::__dependent, _Bind::_Res_type_cv): New helpers to simplify
	return type deduction.
	(_Bind::operator(), _Bind::operator() const): Use new helpers.
	(_Bind::operator() volatile, _Bind::operator() const volatile):
	Likewise. Add deprecated attribute for C++17 mode.
	(_Bind_result::__call): Use std::__invoke.
	(_Bind_result::operator() volatile)
	(_Bind_result::operator() const volatile): Add deprecated attribute.
	(_Bind_helper::__maybe_type, _Bindres_helper::__maybe_type): Remove.
	(_Bind_helper, _Bindres_helper): Don't use _Maybe_wrap_member_pointer.
	(bind, bind<R>): Don't use __maybe_type.
	* src/c++11/compatibility-thread-c++0x.cc
	(_Maybe_wrap_member_pointer): Define here for compatibility symbols.
	* testsuite/20_util/bind/68912.cc: Don't test volatile-qualification
	in C++17 mode.
	* testsuite/20_util/bind/cv_quals.cc: Likewise.
	* testsuite/20_util/bind/cv_quals_2.cc: Likewise.

From-SVN: r241178