https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79820
--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> --- The bug title says std::ifstream sets errno to zero, but it should never run stdio_filebuf::sys_open. Do you have a testcase for this? We should still fix it even if it only affects a non-standard extension, but it's probably not worth backporting if it doesn't affect std::ifstream.
