https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122334
--- Comment #1 from Thomas Schwinge <tschwinge at gcc dot gnu.org> --- Noting just in case that helps to diagnose the underlying issue: the diagnostic/build failure goes away if I locally revert commit r16-3811-gfaae3692f75003f5df226ed776d7386bf848dd00 "libstdc++: Allow std::shared_ptr reference counts to be negative [PR71945]" (after reverting commit r16-4373-g385984f5554a90cd039bf8be1525a63d46ca9750, commit r16-3812-g9a2b1acda0cb2c32568b5ca82996eb0544a3a4ef as prerequisites).
