concatentations that reduce to constants need proper signed-ness
concatentations that reduce to constants need proper signed-ness

It is possible, via the use of the $signed() function, for concatenation
expressions to be signed. Make sure the evaluated constant had the
proper sign by checking explicitly.
themperek/iverilog,themperek/iverilog,CastMi/iverilog,CastMi/iverilog,themperek/iverilog,CastMi/iverilog