How to provide coexisting std::string's (with and without abi:cxx11) in GCC 5.1 and above?

[Jeffrey Walton]

>> Please forgive my ignorance... What is the "coexistence" that is
>> discussed? Naively, I thought it would have been something like this
>> contrived example:
>>
>>   $ cat test.cxx
>>   #include <string>
>>
>>   std::string foo __attribute__ ((visibility ("default")));
>>   std::string bar __attribute__ ((visibility ("default")));
>>
>>   $ g++ -g3 -O2 -shared test.cxx -o test.so
>>
>>   $ nm test.so | grep _Z3
>>   ...
>>   0000201c B _Z3barB5cxx11
>>   00002034 B _Z3fooB5cxx11
>>
>>   $ echo _Z3fooB5cxx11 _Z3barB5cxx11 | c++filt
>>   foo[abi:cxx11]  bar[abi:cxx11]
>>   foo  bar
>>
>> In the above contrived example, foo and bar are in both namespaces.
>> That is, the symbol coexists and "things just work".
>
> Consider the following example:
>
> markus@x4 /tmp % cat test.cpp
> #include <string>
>
> struct Test {
>   __attribute__((used)) std::string foo() { return "foo"; };
> };
>
> markus@x4 /tmp % g++ -c test.cpp && nm test.o | grep _ZN4Test
> 0000000000000000 W _ZN4Test3fooB5cxx11Ev
> markus@x4 /tmp % clang++ -c test.cpp && nm test.o | grep _ZN4Test
> 0000000000000000 W _ZN4Test3fooEv

Exactly! How do I get both _ZN4Test3fooB5cxx11Ev and _ZN4Test3fooEv
into the shared object so both GCC and Clang "just work". I thought
that's what "coexistence" meant, but it appears to mean something else
(that I have not been able to nail down).

Jeff