Fix stack corruption in regrename

[Alexandre Oliva]

On Aug  1, 2001, Bernd Schmidt <bernds@redhat.com> wrote:

>> 
>> Doesn't reload itself use QImode and HImode?  Or is that
>> a bit of history that's vanished?

> That's long gone :)

Oh!  I hadn't realized that.  That was the reason why I had asked
which mode you preferred.

Instead of clearing the modes of all USEs at the beginning, which
might silently break any ports that might have chosen to mark USEs
with modes, for whatever reason (I haven't looked for any), I've
chosen to just make sure no USE is marked at the beginning of reload.
This is the patch I'm currently bootstrapping.  Ok to install, if
bootstrap succeeds?  Ok for 3.0?