PR libstdc++/72792
PR libstdc++/72793
* include/bits/alloc_traits.h (__allocator_traits_base::__rebind):
Replace with class template using void_t.
(__alloc_rebind): Define in terms of
__allocator_traits_base::__rebind.
(allocator_traits): Remove unconditional static_assert for
rebind_alloc.
* include/bits/ptr_traits.h (__replace_first_arg): Remove type member.
(pointer_traits::__rebind): Replace with class template using void_t.
(pointer_traits::rebind): Define in terms of __rebind.
(pointer_traits): Remove unconditional static_assert for rebind.
* testsuite/20_util/allocator_traits/members/rebind_alloc.cc: New test.
* testsuite/20_util/pointer_traits/rebind.cc: New test.
From-SVN: r244680
