Fix placement in carry chains with differing control signals
Fix placement in carry chains with differing control signals

Fixes issues #65 and #87

cseed/arachne-pnr,cseed/arachne-pnr,cseed/arachne-pnr,SymbiFlow/arachne-pnr,SymbiFlow/arachne-pnr,SymbiFlow/arachne-pnr