I do not know of any compiler that forbids C++ comments. Granted, I haven't been contributing to Wine for nearly long enough to be aware of these things, but I've only seen them mentioned under vague terms like "we don't use them in Wine". Even if there isn't a compiler that cares, it's not clear to me whether they're proscribed because of taste (I think I've seen some subsystem maintainers express that, but I can't remember where), or if they'd be perfectly acceptable if anyone cared to use them.
Alexandre, I think this is one of the points Alex is confused about, and is trying to ask for a ruling on. If you feel that this is too minor an issue to give a formal ruling on, fine, I'd just like to make that clarification lest anyone else get too much more frustrated.
C++ comments used to be an issue with some compilers a long time ago, but nowadays it's mostly tradition, and individual taste. Personally I'd rather avoid them, but if some maintainers want to allow them for their subsystems I wouldn't object.