class FFI::Compiler::MultiFileTask

def out_of_date?(timestamp)
    all_prerequisite_tasks.any? do |prereq|
        prereq_task = application[prereq, @scope]
        if prereq_task.instance_of?(Rake::FileTask)
            File.exist?(prereq_task.name) && prereq_task.timestamp > timestamp
        else
            prereq_task.needed?
        end
    end
end