[PATCH] Make std::bind use std::invoke

[Jonathan Wakely <jwakely at redhat dot com>]

I think this is the last place where we weren't using std::__invoke()
for something the standard defines in terms of INVOKE. This should
make all our call wrappers and functional stuff consistent in terms of
support for invoking a pointer-to-member, reference_wrapper etc.

This means we can remove _Maybe_wrap_member_pointer, because
std::__invoke does the right thing for member pointers.

I've also added the deprecated attribute to the volatile overloads,
corresponding to the new wording in C++17:

 "The cv-qualifiers cv of the call wrapper g, as specified below,
 shall be neither volatile nor const volatile."


	* 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.

Tested x86_64-linux, -std=gnu++{14,17},  committed to trunk.

Attachment: patch.txt
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