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PR libstdc++/59768 * include/std/functional (_Unwrap, __invfwd): Define. (__invoke_impl): Remove reference_wrapper overloads and use __invfwd. * include/std/type_traits (__result_of_memobj, __result_of_memfun): Add partial specializations for const reference_wrappers and simplify. * testsuite/20_util/bind/ref_neg.cc: Use dg-excess-errors. * testsuite/20_util/function_objects/invoke/59768.cc: New. From-SVN: r231574