This removes the non-functional garbage colection support from <memory>,
as proposed for C++23 by P2186R2.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
* include/std/memory (declare_reachable, undeclare_reachable)
(declare_no_pointers, undeclare_no_pointers, get_pointer_safety)
(pointer_safety): Only define for C++11 to C++20 inclusive.
* testsuite/20_util/pointer_safety/1.cc: Do not run for C++23.