Fixes #5201.

def bar
end

class Foo
  def bar
    super
  end
end

Foo.new.bar

I believe this code is wrong and shouldn't compile. The consequence is that it fixes #5201, where the method ends up being codegen-ed twice (I believe it tries to codegen the looked-up method because the type of self would have changed, but it doesn't make sense in this case).

This is my first commit touching the compiler itself, hoping for the best.