Okay, it turns out that, in order for this to work, I also need the following
as extern or listed in ruby.h:

  error.c: rb_cNameErrorMesg
  eval.c: rb_cBinding
  eval.c: rb_cMethod
  eval.c: rb_cUnboundMethod
  eval.c: rb_eLocalJumpError
  eval.c: rb_eSysStackError
  eval.c: rb_cCont
  file.c: rb_cStat
  file.c: rb_mFConst
  re.c: rb_eRegexpError
  re.c: rb_cMatch

Everything else I'll probably mock out or leave undefined.

_why