[cond-optab] S/390: Fix conditional trap handling

[Paolo Bonzini]

> To solve this I've replaced the reg:CC operand in condtrap with a
> match_operand allowing to pass a CC register with a different mode.
> 
> Bootstrapped on s390 and s390x with the cond-optab branch.
> 
> I'll apply it tomorrow in case nobody has objections until then.

Go ahead please.

Paolo