https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66146
--- Comment #37 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:9f9dbc8e09cf48406aa24b6c78735f1a7912cc4e commit r11-6229-g9f9dbc8e09cf48406aa24b6c78735f1a7912cc4e Author: Jonathan Wakely <jwak...@redhat.com> Date: Thu Dec 17 13:16:02 2020 +0000 libstdc++: Fix -Wunused warning As noted in PR 66146 comment 35, there is a new warning in the new std::call_once implementation. libstdc++-v3/ChangeLog: * src/c++11/mutex.cc (std::once_flag::_M_finish): Add maybe_unused attribute to variable used in assertion.