https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99832
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> --- The addition to c++config.h works need to be before os_defines.h is included. But as I said I'm comment 2, I don't think either of the suggestions in comment 1 works. IIRC the way glibc ended up doing the time_t transition provides no way for libstdc++ to detect what it needs to know (which is not whether time_t is 64 bits, but whether it has *changed* from 32 to 64 bits).
