[RFA] Move cpplib to the toplevel

[Paolo Bonzini]

> I don't think this patch is appropriate, as libiberty's hashtab was
> NOT copied from cpplib at the time it was copied.  I'm not a big fan
> of retroactively changing history like this.

I can change the wording, is something like

  This hash is the same as that in libcpp's symtab.c.  Zack had the
  following to say with respect to applicability, though note that unlike
  symtab.c (which at the time was gcc/hashtable.c), this hash table
  implementation re-hashes rather than chain buckets.

ok for you?

Paolo