This implements the C++23 change "Poison Pills are Too Toxic". This
makes sense to do unconditionally for C++20, as the corner cases that it
fixes are considered to be defects in the C++20 design (e.g. LWG3480 was
needed to fix directory iterators because of these pills being too
toxic).
libstdc++-v3/ChangeLog:
* include/bits/iterator_concepts.h (__imove::iter_move): Define
poison pill as deleted for consistency.
(__access::begin): Replace with a single declaration.
* include/bits/ranges_base.h (__access::end, __access::rbegin)
(__access::rend, __access::size): Likewise.
* include/bits/version.def (ranges): Update value for C++23.
* include/bits/version.h: Regenerate.
* libsupc++/compare (__compare): Add missing poison pill
overloads.
* testsuite/std/ranges/version_c++23.cc: Adjust expected value
of __cpp_lib_ranges.
* testsuite/std/ranges/access/p2602.cc: New test.
