[IR] Fix for InterpretedIRBlockBody parameterList regression

* Right now, InterpretedIRBlockBody is built when IRClosure is
  built which is too early for passing in parameterList into the
  InterpretedIRBlockBody constructor.

  Maybe we should set up begin/end phases for scope construction
  and build the body as part of the end phase, which lets us get
  rid of the setParameterList method I added here.

* rubyspec run is back to 10 failures and 3 errors now.