cxxrtl: don't crash generating debug information for unused wires.
cxxrtl: don't crash generating debug information for unused wires.

antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,antmicro/yosys,cliffordwolf/yosys,antmicro/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,cliffordwolf/yosys,antmicro/yosys,antmicro/yosys,cliffordwolf/yosys,cliffordwolf/yosys,YosysHQ/yosys,antmicro/yosys,antmicro/yosys,YosysHQ/yosys,cliffordwolf/yosys,YosysHQ/yosys,cliffordwolf/yosys,cliffordwolf/yosys,cliffordwolf/yosys,YosysHQ/yosys,YosysHQ/yosys