https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24012
--- Comment #38 from Gerald Pfeifer <gerald at pfeifer dot com> --- Yes. The original need to define _POSIX_C_SOURCE to get to fileno on FreeBSD is gone with FreeBSD 14 (and probably several versions before that). #define _POSIX_C_SOURCE 1 triggers all sorts of other issues there, and the fix is simple: use #define _POSIX_C_SOURCE 200809 or the like instead (*if* _POSIX_C_SOURCE is necessary at all).
