Hi

With the recent fixes to std::vector implementation all 23_containers 
and 25_algorithms tests are passing in C++98 and C++20 modes.

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 functor-aware
algos. It forces to have iterators dereferenced at algo level and not in the
predefined functors anymore.

Also make sure that in algos implementation details functors are passed by
reference rather than by copy.

libstdc++-v3/ChangeLog:

         * include/bits/move.h
         (_GLIBCXX_FWDREF): Now substituted by a lvalue-reference in 
pre-c++11 mode.
         (_GLIBCXX_FWDCREF): New macro, substituted by a const lvalue 
reference in
         pre-c++11 mode.
         * include/bits/stl_tree.h: Replace _GLIBCXX_FWDREF usage by 
_GLIBCXX_FWDCREF.
         * include/std/functional: Include predefined_ops.h.
         (_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. Replace usage of
         std::ref by std::move to pass predicate to std::__remove_if.
         * include/std/string: Likewise.
         * include/std/vector: Likewise.
         * src/c++17/memory_resource.cc: Include <functional>.

I'm not proud of the _GLIBCXX_FWDCREF but I'm sure you'll find a better 
name !

Ok to commit once I've completed the test coverage ?

François