[#60781928] Explicitly add search paths for embedded ruby

I originally intended to implement this with RUBYLIB_PREFIX, but

1. The environment variable is listed as deprecated (even though it's still in ruby 2.0)
2. True to ruby's form it was causing an memory error when trying to use it.

So instead I set the paths following the pattern that ruby uses internally during the ruby init block.

@axelstudios @evanweaver