https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109818
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- Hmm, I don't see anything in the configure scripts that would cause c_std to be used implicitly for djgpp (or any other target). Maybe there's a local patch applied to the djgpp copy of GCC sources? It might set C_INCLUDE_DIR explicitly, or adjust the default chosen for GLIBCXX_ENABLE_CHEADERS in libstdc++-v3/acinclude.m4
