[Bug libstdc++/79798] New: [7 Regression] std::bind uses wrong value category with result_of

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79798

            Bug ID: 79798
           Summary: [7 Regression] std::bind uses wrong value category
                    with result_of
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

Another case like PR 79486, this fails to compile with trunk:

#include <functional>

struct X { };
const X f(int);

struct Y {
  void operator()(X&&) = delete;
  int operator()(const X&&);
};

auto b = std::bind(Y(), std::bind(f, std::placeholders::_1));
auto i = b(1);


x.cc:12:13: error: no match for call to ‘(std::_Bind<Y(std::_Bind<const X
(*(std::_Placeholder<1>))(int)>)>) (int)’
 auto i = b(1);
             ^