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

[Jonathan Wakely]

On 24 March 2016 at 11:55, Jeffrey Walton wrote:
> In the test program below, why does -Wabi-tag trigger a warning with
> the std::string when using -std=c++03?

"Although the changes were made for C++11 conformance, the choice of
ABI to use is independent of the -std option used to compile your
code, i.e. for a given GCC build the default value of the
_GLIBCXX_USE_CXX11_ABI macro is the same for all dialects. This
ensures that the -std does not change the ABI, so that it is
straightforward to link C++03 and C++11 code together. "

https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html