* sysdeps/unix/sysv/linux/renameat.c: Move errno setting code in

* sysdeps/unix/sysv/linux/renameat.c: Move errno setting code in

	separate function __atfct_seterrno_2.
	* include/fcntl.h: Declare __atfct_seterrno_2.
	* posix/unistd.h: Declare linkat, symlinkat, readlinkat.
	* io/Makefile (routines): Add linkat, symlinkat, readlinkat.
	* io/Versions [GLIBC_2.4]: Export linkat, symlinkat, readlinkat.
	* io/linkat.c: New file.
	* io/readlinkat.c: New file.
	* io/symlinkat.c: New file.
	* sysdeps/unix/sysv/linux/linkat.c: New file.
	* sysdeps/unix/sysv/linux/readlinkat.c: New file.
	* sysdeps/unix/sysv/linux/symlinkat.c: New file.