[Sim] Large patch to sim/common/genmloop.sh

[Doug Evans]

Ben Elliston writes:
 >    Except for minimizing the amount of changes, is there any reason to
 >    keep the cpu prefix?
 > 
 > Yes.  In some contexts (namely modelling), it makes sense to refer to @cpu@:
 > 
 > 	#define WANT_CPU_@CPU@
 > 	[...]
 > 	@cpu@_model_insn_before (current_cpu, first_p);
 > 	[etc].
 > 
 > But correct me if I am mistaken.

Ah.

You may or may not want different versions of these for each ISA.
I kinda hate to have both prefix and cpu if one will do.