_SC_XOPEN_VERSION  623 ext/etc/constdefs.h #if !defined(_SC_XOPEN_VERSION)
_SC_XOPEN_VERSION  625 ext/etc/constdefs.h #  define _SC_XOPEN_VERSION _SC_XOPEN_VERSION
_SC_XOPEN_VERSION 1313 ext/etc/constdefs.h #if defined(_SC_XOPEN_VERSION)
_SC_XOPEN_VERSION 1314 ext/etc/constdefs.h     rb_define_const(mod, "SC_XOPEN_VERSION", INTEGER2NUM(_SC_XOPEN_VERSION));