Add vpip_calc_clog2 to vvp.def file
Add vpip_calc_clog2 to vvp.def file

This is needed to get cygwin to compile correctly.

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