* io/Makefile (routines): Add openat and openat64.
(tests): Add tst-openat.
* io/Versions: Add openat and openat64 for GLIBC_2.4.
* sysdeps/generic/openat.c: New file.
* sysdeps/generic/openat64.c: New file.
* sysdeps/unix/sysv/linux/openat.c: New file.
* sysdeps/unix/sysv/linux/openat64.c: New file.
* io/tst-openat.c: New file.
* sysdeps/unix/sysv/linux/device-nrs.h: Add info for /dev/full.