rtlsim: handle ctrl-c more gracefully.
bootrom: pad to full size.

This silences icarus warnings like:

WARNING: ./sim_dp_rom.v:20: $readmemh: Standard inconsistency, following
1364-2005.
rtlsim: fixup lxt2 generation
rtlsim: make trace debugging disabled by default.

Add --debug to oldland-rtlsim so we don't create traces by default which
gives a nice simulation speed improvement.
verif: always rebuild iverilog model.

We use icarus verilog command files and getting dependencies is tricky.
Compilation time is tiny and rather than duplicating deps, just rebuild
each time.