Spice reader: .global should not add pin if the signal isn't used in a subcircuit

[klayoutmatthias]

Example:

.global VDD VDDA VSS

.subckt inv A Z
MN N0 A VSS VSS NMOS W=1u L=1u
MP N0 A VDD VDD PMOS W=2u L=1u
.ends inv

In this case, VDDA should not be made a pin for the inv subcircuit.