One thing people never seem to mention is how dead simple it is to cross-compile Go code. For me to consider Nim or Rust, I need to know that I can do something as simple as GOARCH=arm GOOS=linux go build.
Since Nim uses C as an intermediate representation, cross-compilation support should be as good as your C compiler's.
Rust's cross-compilation seems to not be that great at the moment. Although i believe that's because it hasn't been done yet, rather than having been done badly.
Rust's cross-compilation works, but it's not as easy as it could be. One issue is that you need a cross-compiled version of the standard library lying around.
On the other hand, if you run "an unsupported Unix" that implies you are a bit more tech-savvy (and willing to put in the effort) than most when it comes to these issues.