The hash value of a Method must remain constant after a compaction, otherwise
it may not work as the key in a hash table.

For example:

    def a; end

    # Need this method here because otherwise the iseq may be on the C stack
    # which would get pinned and not move during compaction
    def get_hash
      method(:a).hash
    end

    puts get_hash # => 2993401401091578131

    GC.verify_compaction_references(expand_heap: true, toward: :empty)

    puts get_hash # => -2162775864511574135