Update $clog2() to add support for two-state variables.
Update $clog2() to add support for two-state variables.

The $clog2() routine can consider any two state variable argument
as numeric.

themperek/iverilog,CastMi/iverilog,themperek/iverilog,themperek/iverilog,CastMi/iverilog,CastMi/iverilog