After committing it I noticed I'd also accidentally added a change to
__synth3way as well, which I meant to do in a separate commit. I've
updated the changelog entry to reflect that additional change.
* libsupc++/compare (__detail::__synth3way): Add noexcept-specifier.
* include/std/version (__cpp_lib_three_way_comparison): Update value.
* libsupc++/compare (__cpp_lib_three_way_comparison): Likewise.
+ (__detail::__synth3way): Add noexcept-specifier.
* include/bits/stl_map.h (map): Define operator<=> and remove
operator< for C++20.