Hurd largefile interfaces

[Mark Kettenis]

I implemented most of the largefile interfaces for the Hurd.  These
are essentially stubs that use the old RPCs (the Hurd "equivalent" of
system calls) and convert the return values to the appropriate type,
just like we do on Linux when a particular LFS system call is absent.

glob64 is still missing, but everything that's necessary to implement
it is present.  Ulrich, could you please move glob64.c from
sysdeps/unix/sysv/linux to sysdeps/gnu?  If you don't want to do that
right now (close before the 2.2.1 release), we can do it later.  But
please tell me what you decide, such that I can temporarily put a
glob64.c in sysdeps/mach/hurd that includes the Linux-specific file.

Mark