Cleanup _Rb_tree_impl in versioned namespace

[Jonathan Wakely]

On 22/01/17 22:14 +0100, François Dumont wrote:
>Hi
>
>    Jonathan proposed to leverage on versioned namespace to do some 
>abi breaking change so here is one simple on _Rb_tree_impl.
>
>    I wonder if versioned namespace should be bump for this change. Do 
>we really have any kind of abi compatibility for versioned namespace ? 
>I guess not but so why a versioned namespace ?
>
>    Tested under x86_64 linux, ok to commit ?

I know it's a tiny change, but let's wait for Stage 1:
https://gcc.gnu.org/ml/gcc/2017-01/msg00181.html

For GCC 8 I plan to switch the versioned-namespace to use the __cxx11
ABI, and bump the soname to libstdc++.so.8 and change the versioned
namespace to __8. This kind of change would be a great idea to do at
the same time.