opt_expr: more fixes for $xor/$xnor
opt_expr: more fixes for $xor/$xnor

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