Unable to install rbs on JRuby

[mrckzgl]

It seems rbs is trying to make a native extension on JRuby which is not supported.
For complete log output, see Shopify/ruby-lsp#2292
That results in rbs not being able to be installed in a JRuby environment, gem install rbs will fail in such.

[headius]

FWIW we (JRuby) very much want to support rbs and I'm sure it is possible to do so. We just don't have a lot of dev resources right now.

[headius]

The piece in the extension is the C-based parser, which replaced the old racc-based pure-Ruby parser in #788.

While the extension could possibly be ported to Java, it's quite a lot of work. It might be faster to revive the racc parser and try to update it.