Generating CPU family headers for multiple isas

[Ben Elliston]

   Hm, that reminds me.  Does it make much sense to have isa-specific
   hardware?  I can see some cgen-time error checking (to keep isa
   semantics limited to isa-visible hardware/operands), but at run time,
   generating a single unified struct of all isas' hardware seems
   appropriate.

I think it makes sense to do so, yes.

I agree that a single unified struct would be good, but remember that,
again, a cgen user should not be forced into choosing alternative names for
hardware elements just to maintain uniqueness.  It makes just as much sense
for the ARM isa to have a h-gr element as it does for Thumb.

Ben