in Verilog source code. Also add two parameters to d_cosim:
sim_args is used to pass string arguments to a Verilator simulation;
and lib_args is for future use. In vlnggen, also check for two causes
of failure: a verilator error may lead to creation of interfering header
files; and misleading instances of verilated_shim.cpp can cause an obscure
failure (reported by Diarmuid Collins).
Use a generic name for the generated DLL in MSVC.CMD.
Giles Atkinson
693a9df09f