Why does -Wabi-tag complain when -std=c++03?

[Jeffrey Walton]

>>> The new std::string and std::list are also valid implementations for C++03.
>>
>> OK, good. Thanks.
>>
>> If its a valid implementation, then why is the compiler complaining?
>
> That question doesn't even make sense. GCC's warnings aren't there to
> say "this implementation does not conform to the standard".

Yeah, it only get worse:

$ g++ -x c++ -include iostream -dM -E - </dev/null | grep ABI_CHANGE
$ g++ -x c++ -include iostream -std=c++11 -dM -E - </dev/null | grep ABI_CHANGE
$

I get the problem its trying to solve; especially the part about the
return type ABI. But I have to admit I'm just about totally confused
about the implementation details for library authors, the coexisting
symbols discussed in the blog, and the ABI_CHANGE change macro.

Jeff