* Ruby contains some things generated by bison or such.

It seems the generated parse.c file (from parse.y) is included in the
tarballs as a service to workaround a bootstrap problem; generating the
parser requires ruby.  See also:

  https://github.com/ruby/ruby/blob/master/common.mk#L910

See my other reply, and also:

Even if generating the .c from the .y from the Ruby code would be ideal, at least generating the .c from the .y (and using the pre-generated the .y) is still an improvement, it would at least help with the 'buggy bison' scenario.

Greetings,
Maxime.