[patch] adjust libgloss addresses for 64-bit

[Eric Christopher]

> >  So what should "la $2,0x80000000($3)" do when using 64-bit addresses?  
> > Replace/supplement the offset with a symbol as suitable...
> 
> Hm, looks like we break somebody's assumptions regardless what we do.
> So leaving la as it is and warn about its use seems to be best.


To warn we should do two things:

1) Turn HAVE_64BIT_OBJECTS back to HAVE_64BIT_ADDRESSES in do_la.
2) Warn if we have O_constant as the type and it isn't a sign-extended
32-bit number.

-eric