In most cases, these things would work, but not here. Tried everything, nothing works except using a pre-modules-compiler.
In general, golang seems to work best with golang-only projects. As soon as there are other languages in the mix, like C++ here, things get very ugly very fast.
Ah, I think I misinterpreted what you meant by "nothing works anymore". I thought you were saying that no old Go projects were usable with new Go compilers. I believe you that this particular project may not work with the current toolchain.
Ah, yes, that wasn't sufficiently clear in my text. In almost all projects I've done/used, go modules work fine and are nice. It is just this one library that I know ceased to work.