https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88736
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- No, it's the same issue. The reason that <cstddef> declares it there is because <cstddef> includes <stddef.h> and GCC's <stddef.h> declares ::nullptr_t. We cannot remove it from <cstddef> without removing it from <stddef.h>, and that's what the unresolved library issue is about.
