hurd: Add renameat2 support for RENAME_NOREPLACE

	* include/stdio.h (__renameat2): New hidden prototype.
	* stdio-common/renameat2.c (__renameat2): Add hidden definition.
	* sysdeps/mach/hurd/renameat.c (__renameat): Move implementation to...
	* sysdeps/mach/hurd/renameat2.c (__renameat2): ... new function, and
	add support for RENAME_NOREPLACE.
	* sysdeps/unix/sysv/linux/renameat2.c (__renameat2): Add hidden definition.