A patch for visibility.

[Martin von Loewis]

> When we decided to use those bits for visibility, those bits will
> be used for visibility and nothing else. If some systems uses them
> for other purposes, they are broken and should be fixed.

On a architectural level, I agree. However, when I submitted my first
set of visibility patches, I noticed that some systems "need to be
fixed", then. I'd rather see them fixed first, instead of silently
breaking them.

Of course, since most of those are Cygnus-maintained ports, it's
ultimately up to Cygnus to voice an opinion.

Regards,
Martin