maint: use pragma consistently across replacement headers Several headers set #pragma GCC system_header prior to checking any multiple inclusion guards; maintenance is easiest if all replacement headers follow the same paradigm. * lib/ctype.in.h (system_header): Hoist for consistent placement. * lib/dirent.in.h (system_header): Likewise. * lib/errno.in.h (system_header): Likewise. * lib/float.in.h (system_header): Likewise. * lib/getopt.in.h (system_header): Likewise. * lib/iconv.in.h (system_header): Likewise. * lib/inttypes.in.h (system_header): Likewise. * lib/langinfo.in.h (system_header): Likewise. * lib/locale.in.h (system_header): Likewise. * lib/math.in.h (system_header): Likewise. * lib/netdb.in.h (system_header): Likewise. * lib/netinet_in.in.h (system_header): Likewise. * lib/pty.in.h (system_header): Likewise. * lib/sched.in.h (system_header): Likewise. * lib/se-selinux.in.h (system_header): Likewise. * lib/search.in.h (system_header): Likewise. * lib/spawn.in.h (system_header): Likewise. * lib/stdarg.in.h (system_header): Likewise. * lib/stdint.in.h (system_header): Likewise. * lib/string.in.h (system_header): Likewise. * lib/strings.in.h (system_header): Likewise. * lib/sys_file.in.h (system_header): Likewise. * lib/sys_ioctl.in.h (system_header): Likewise. * lib/sys_socket.in.h (system_header): Likewise. * lib/sys_times.in.h (system_header): Likewise. * lib/sys_utsname.in.h (system_header): Likewise. * lib/sys_wait.in.h (system_header): Likewise. * lib/sysexits.in.h (system_header): Likewise. * lib/unistd.in.h (system_header): Likewise. * lib/wctype.in.h (system_header): Likewise. Signed-off-by: Eric Blake <eblake@redhat.com>