Section D.5
Whoever the user that is posting the content is agreeing to the terms of service. If they don't actually have permission to agree to those terms with the content, then where that liability falls will likely fall to a court, but I'm sure I would argue as a user who forked the content, that I was given permission via the TOS which has to be followed by the user posting the content.
That ToS is between wimamp and GitHub, not you.
You have to do the due diligence to get the permission from winamp.
You might be able to get away by suing GitHub and have them sue winamp. ..
TOS are not just fluff and paper, but legally binding. Granted, when there is a conflict between two conflicting requirements, it's never clear cut, but it's not just "GitHub will be mad."