[wwwdocs] Link from gcc-4.{6,7}/changes.html to porting_to.html

[Gerald Pfeifer]

Hi Tobias,

On Thu, 12 Jan 2012, Tobias Burnus wrote:
> I intent to commit the attached patch to link

I believe Benjamin committed this yesterday, right?  Thanks for
raising the issue, these links are good to have.

Gerald