I've tried to compile Libcello with cosmopolitan with little to no success, I don't think the Ruby runtime will be any easier sadly.

Could also be a skill issue.

Would you be able to expand on this, my impression is that these tools build a custom c program instead? Thanks

They provide a compiler and bundled userland that can be used to compile many C programs (even, for example, a slightly patched CPython) for a multi-OS binary distribution. Ruby shouldn't be that different.