cxxrtl: don't assert on wires with multiple drivers.
cxxrtl: don't assert on wires with multiple drivers.

Fixes #2374.

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