https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115907
--- Comment #20 from Arsen Arsenović <arsen at gcc dot gnu.org> --- (In reply to cqwrteur from comment #17) > Then why? Why does it define _ISOC2X_SOURCE? C++ is not even C. "it"? presuming you mean glibc, because _GNU_SOURCES enables all features, including the C2X specific ones. note that not enabling those would not fix downgrading being broken.