[wwwdocs] Update links to C++ ABI

[Gerald Pfeifer]

On Sun, 26 Aug 2012, Ian Lance Taylor wrote:
>> It used to be http://sourcery.mentor.com/public/cxx-abi/ as of lately,
>> and now redirects to http://mentorembedded.github.com/cxx-abi/ .
>>
>> I went ahead and updated all our references per the patch below.
> I don't think that is wise.  The document itself promises that the
> permanent URL is http://codesourcery.com/cxx-abi/ .  No other URL is
> promised to be permanent.  I think we should link to the permanent URL
> as long as it continues to work.

Well, the document itself also carries "Revised 20 March 2001" in
line 2. ;-)

Mark, any recommendation from your side?  Is it fine to refer to 
the new mentorembedded.github.com address?

(Linking to a page that redirects makes verifying the accuracy of
links tricky.)

Gerald