OpenBSD has none of those languages in the base OS; given they won't update gcc or switch to clang, Lua is the only one that they could support (NetBSD has it in base) but there is not a lot of system software written in Lua (alas). It doesn't have a depth of libraries that Go does. JavaScript would probably never pass review, so Rust is possibly a future option, unless a system programming community springs up around Lua.
FWIW, the default Go compiler doesn't depend on GCC or Clang, and doesn't do as many optimizations which could be dangerous or buggy, which I gather is the main problem with adopting LLVM?