Add Verilator 5.004 to CI

[jackkoenig]

This PR is partially to demonstrate that Verilator 5.004 (and probably 5.002 but I haven't tested it) does not work with the Verilator JNA stuff. I have debugged a bit, here's what I know:

Individual tests or tests that pass seem to work, but if you have multiple tests in a row in the same JVM, it will hang when trying to close the NativeLibrary on this line:

chiseltest/src/main/scala/chiseltest/simulator/jna/JNAUtils.scala

Line 136 in 78b0f28

so.close()

Verilator 5 added support for SystemVerilog timing constructs, so my understanding is that it's a massive change to the underlying threading implementation.

My suspicion is that something has changed about how we should terminate the simulation--that there's some child thread running that isn't being stopped and is preventing JNA from closing the shared library. This is purely conjecture though, so take it with a grain of salt.

[ekiwi]

Verilator 5 added support for SystemVerilog timing constructs, so my understanding is that it's a massive change to the underlying threading implementation.

I thought that by default the new timing feature would be off, but could not find any confirmation on that. You could try passing --no-timing.

The number of threads should also be 1 be default: https://verilator.org/guide/latest/exe_verilator.html#cmdoption-threads

[ekiwi]

One possible source of the problem could be that Verilator 5 now makes all simulations "thread-safe", which could mean thread local variables which might not play well with the library loading and unloading. This is more of an uneducated guess though.