* sysdeps/mach/hurd/fchmodat.c: New file.
* sysdeps/mach/hurd/fchownat.c: New file.
* sysdeps/mach/hurd/fxstatat.c: New file.
* sysdeps/mach/hurd/fxstatat64.c: New file.
* sysdeps/mach/hurd/linkat.c: New file.
* sysdeps/mach/hurd/mkdirat.c: New file.
* sysdeps/mach/hurd/openat.c: New file.
* sysdeps/mach/hurd/openat64.c: New file.
* sysdeps/mach/hurd/symlinkat.c: New file.
* sysdeps/mach/hurd/unlinkat.c: New file.
* sysdeps/mach/hurd/xmknod.c (__xmknod): Just call __xmknodat.
Guts move to ...
* sysdeps/mach/hurd/xmknodat.c: ... here, new file.
* hurd/lookup-at.c: New file.
* hurd/Makefile (routines): Add it.
* hurd/hurd/fd.h: Declare __file_name_lookup_at,
__file_name_split_at and __directory_name_split_at.
* hurd/hurd/lookup.h: Declare {,__}hurd_directory_name_split.
* hurd/hurdlookup.c (__hurd_directory_name_split): Use __memrchr
unconditionally.
* sysdeps/mach/hurd/open.c: Define {,__,__libc_,}open64 as aliases.
* sysdeps/mach/hurd/open64.c: New file.
