http://ifosslawbook.org/france/ ("Moral Rights" heading)
All rights granted under this License are granted for the
term of copyright on the Program, and are irrevocable
provided the stated conditions are met.
I don't know how this affects the GPL specifically, but you can be pretty sure that if the GPL doesn't contain France-specific French-language legalese to work around it, then it's likely to be revokable whatever the license says. Of course this only affects you if you're in France or have French contributors.
If that's the law in France, it trumps the license text.
Just as the law trumps any clause requiring the sacrifice of the licensee's firstborn on an altar.
If conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License. If you cannot convey a
covered work so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you may
not convey it at all.
> Nevertheless, the Intellectual Property Code provides some specific rules regarding moral rights over software. It provides that the author may not oppose modifications of the software, in as far as such modifications do not affect his honor or reputation, and exercise his right of withdrawal.
The remaining issue is that you can still forbid modifications that "affect your honor or reputation".
[1] http://legifrance.gouv.fr/affichCodeArticle.do?cidTexte=LEGI...