https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118700
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- https://gcc.gnu.org/onlinedocs/cpp/Invocation.html#index-fno-canonical-system-headers https://gcc.gnu.org/onlinedocs/gcc/Preprocessor-Options.html#index-fno-canonical-system-headers There is not enough documentation to say what this option does though.
