Clean up `exec` code according to review.
Clean up `exec` code according to review.

Co-Authored-By: Miodrag Milanović <5995fc0bb21e0f60291ee6b04dc42a78e4c347a4@gmail.com>

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