Good idea. [Here's my attempt at this](https://gist.github.com/anonymous/e0a225a0fb8f0574ff82aaf51266a091)
Does seem to reproduce the same issue:
$ nim c -r repro.nim
Will it work?
It worked!
$ nim c -r --threads:on repro.nim
Will it work?
<hangs indefinitely>
See anything I'm missing? If not I'll figure out how to file as an issue.
