Fix a long-standing bug in the IO-PORT SETF builtins.
Fix a long-standing bug in the IO-PORT SETF builtins.

They would crash the compiler if the result value was used and the port
was a ub8 constant.

varjagg/Mezzano,rvedam/Mezzano,AugustusHuang/Mezzano,AugustusHuang/Mezzano,froggey/Mezzano,varjagg/Mezzano,rvedam/Mezzano,froggey/Mezzano