Fix gnu versioned namespace mode 00/03

[Iain Sandoe]

Hi François

> On 4 May 2024, at 22:11, François Dumont <frs.dumont@gmail.com> wrote:
> 
> Here is the list of patches to restore gnu versioned namespace mode.
> 
> 1/3: Bump gnu version namespace
> 
> This is important to be done first so that once build of gnu versioned namespace is fixed there is no chance to have another build of '__8' version with a different abi than last successful '__8' build.
> 
> 2/3: Fix build using cxx11 abi for versioned namespace
> 
> 3/3: Proposal to default to "new" abi when dual abi is disabled and accept any default-libstdcxx-abi either dual abi is enabled or not.
> 
> All testsuite run for following configs:
> 
> - dual abi
> 
> - gcc4-compatible only abi
> 
> - new only abi
> 
> - versioned namespace abi

At the risk of delaying this (a bit) - I think we should also consider items like once_call that have broken impls. in the current library - and at least get proposed replacements available behind the versioned namespace; rather than using up a namespace version with the current broken code.

I have a proposed once_call replacement (but I think Jonathan also has one or more alternatives there)

Please can we try to identify any other similar blocked fixes?

Iain