gcc/intl vs. src/intl

[DJ Delorie]

> Presumably the long-term fix would to keep intl in sync as we keep
> libiberty in sync.

Note: the key to doing this is automatically to let one repository
(presumably, src) relinquish control of src/intl to the other (gcc),
so that the sync scripts only have to work one way.  We do this for
libiberty.

Keeping them in sync automatically is not practical if patches are
allowed on both sides.  This is the case for toplevel.