[wwwdocs] Update changes.html with libstdc++ changes

[Gerald Pfeifer]

On Wed, 8 Apr 2015, Jonathan Wakely wrote:
>> The only drawback of this, and some similar cases, is that we now
>> risk referring to older versions on a release branch.
> Yes, I realised that problem when making the change and linking to the
> versions that were current at the time. One option would be to add a
> gcc-4.8 symlink that points to the latest gcc-4.8.x version, but that
> adds more work for the release managers and only has a small benefit.

Agreed.

> Alternatively, since we only tend to have four or five releases from a
> branch, we could just update them manually when we remember to. That's
> only necessary until the branch closes, at which point the latest
> release won't change. It's not a huge problem if the links don't go
> to the latest docs immediately IMHO.

Agreed, and agreed.  Let's just keep an eye on it and (try to)
update when a new release of an existing branch comes out.

Gerald