Alright, I was able to successfully dynamically link ARC against Ruby 1.8.7. This is most probably a temporary solution for now. There are some weird problems when I try to statically link Ruby 1.8.7, some functions don't seem to be implemented like they are described in the headers. :/
With Ruby 1.9.2 I had the continuous problem that I couldn't get the interpreter running. Each time I tried to initialize and run an interpreter node, it wouldn't work.
I have also committed the file test.rb in the root directory which is then read and executed. Sadly, I don't know how to get out of the interpreter main loop yet as it doesn't seem to stop after all scripts have been executed.
In any case, our final goal is to compile a minimalistic Ruby 1.9.2 and then to compile ARC and statically link it against that static library. For now, we will work with what we have here.
EDIT: I probably did this in record time compared to anybody else who tried it in the RMXP community. #_# It took me 3 hours today and I think 3 more hours the other day where I mainly wasted time compiled Ruby. And if I had tried it with Ruby 1.8.7 right away, I probably would have done it in under an hour since there is a proper documentation how to do it in Ruby 1.8.x while for Ruby 1.9.x there is none. :/