https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88264
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> --- This can't be done safely in libstdc++ because we can't call getenv safely. We could be dlopened while another thread is calling setenv. But if that could be solved, other useful tunables would be the filenames to use for chrono::tzdb (for tzdata.zi and leapseconds), and formatting options for the default contract violation handler (e.g. human readable vs log-friendly).
