[Patch] Rename --enable-visibility to --enable-libstdcxx-visibility, adjust docs

[Jonathan Wakely]

On 8 November 2011 13:08, Paolo Carlini wrote:
> Hi,
>
> this is what I'm finishing testing. Jon, is the updated documentation good
> enough?

That new wording looks good to me.  My only comment would be that as
it says "In 4.2 and later" it might be worth adding "Prior to 4.7 this
option was spelled --enable-visibility" to the end.