Run _kompile in parallel when --with-llvm-library is present

[anvacaru]

Perhaps, it is worth using the multiprocessing lib on the two calls to _kompile [here].(https://github.com/runtimeverification/evm-semantics/blob/master/kevm-pyk/src/kevm_pyk/foundry.py#L398)

[ehildenb]

I think instead we should ask the K frontend team to just always compile the haskell backend with the booster and build the LLVM library for it as well. The booster backend should become the default.

[anvacaru]

closing this as duplicate of #1939.