First attempt at an incisive backend

[Jbalkind]

I mainly copy and pasted from the VCS backend. Happy to modify however is best. It seems to run my simple tests at least.

[cmarqu]

Maybe https://github.com/VUnit/vunit/blob/master/vunit/incisive_interface.py can be a source of inspiration as well. It uses the irun executable and can e.g. hand defines/generics to it (via -define and -gpg respectively).

[olofk]

Should we drop this one now that there's a xcelium backend?

[Jbalkind]

I thought the xcelium backend didn't support incisive though?

[olofk]

I would say that's a pretty good argument

From my (somewhat limited) understanding, these tools have a lot in common. Can we benefit from this somehow or are we just as well to have two independent backends?

[Jbalkind]

To be clear, I'm not tied at all to this PR. I don't know the tool that well and just need the ability to run the simulations I can already run independently of fusesoc in order to port openpiton to fusesoc. This PR may not even work today and it could be that sharing the xcelium backend would be a better idea. But I remember that you previously commented that keeping them separate was fine (https://github.com/olofk/fusesoc/issues/272#issuecomment-494933700) so maybe we could just copy and adapt it? I don't know.