I think we all agree that __gnu_cxx::__ops needed to be reimplemented, 
here it is.

Note that I kept the usage of std::ref in <string>, <vector> and <deque>.

     libstdc++: Reimplement __gnu_cxx::__ops operators

     Replace functors using iterators as input to adopt functors that
     are matching the same Standard expectations as the ones imposed on
     predicates used in predicates-aware algos. Doing so we need far less
     functors. It impose that iterators are dereference at algo level and
     not in the functors anymore.

     libstdc++-v3/ChangeLog:

             * include/std/functional (_Not_fn): Move to...
             * include/bits/predefined_ops.h: ...here, and expose a version
             in pre-C++14 mode.
             (__not_fn): New, use latter.
             (_Iter_less_iter, _Iter_less_val, _Val_less_iter, 
_Iter_equal_to_iter)
             (_Iter_equal_to_val, _Iter_comp_iter, _Iter_comp_val, 
_Val_comp_iter)
             (_Iter_equals_val, _Iter_equals_iter, _Iter_pred, 
_Iter_comp_val)
             (_Iter_comp_to_val, _Iter_comp_to_iter, _Iter_negate): Remove.
             (__iter_less_iter, __iter_less_val, __iter_comp_val, 
__val_less_iter)
             (__val_comp_iter, __iter_equal_to_iter, 
__iter_equal_to_val, __iter_comp_iter)
             (__val_comp_iter, __iter_equals_val, __iter_comp_iter, 
__pred_iter): Remove.
             (_Less, _Equal_to, _Equal_to_val, _Comp_val): New.
             (__less, __equal_to, __comp_val): New.
             * include/bits/stl_algo.h: Adapt all algos to use new 
__gnu_cxx::__ops operators.
             When possible use std::move to pass predicates between 
routines.
             * include/bits/stl_algobase.h: Likewise.
             * include/bits/stl_heap.h: Likewise.
             * include/std/deque: Cleanup usage of __gnu_cxx::__ops 
operators.
             * include/std/string: Likewise.
             * include/std/vector: Likewise.

Tested under Linux x86_64 normal and _GLIBCXX_DEBUG modes.

Ok to commit ?

François