https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84980
--- Comment #1 from Volker Reichelt <reichelt at gcc dot gnu.org> --- That's of course "-fconcepts" instead of "-fconcpets".
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84980
--- Comment #1 from Volker Reichelt <reichelt at gcc dot gnu.org> --- That's of course "-fconcepts" instead of "-fconcpets".