I am not sure why the copyright clerk forwarded this to the general GCC mailinglist instead of helping you obtain an assignment form, but we can proceed anyway.
Do you work for any university or company that could claim ownership of your code? If no, you directly can assign your code. If yes, we need to work with that organization as well through an assignment and/or disclaimer. Please let me know the situation and I can send you the proper form for you to request a pre-written assignment form from the FSF. Thanks, David