Garbage collector is again available for Alpha (finally)

[Christopher C Chimelis <chris@classnet.med.miami.edu>]

Now that alpha has a libgc package that supposedly works, I'll go ahead
and test compile gcc again allowing libobjc to finally have garbage
collection on Alpha. I'll give you the results of this.  If it does work,
we can re-enable that option for building gcc.

C