[PATCH] libstdc++: Add C++2a synchronization support

[Stephan Bergmann]

On 20/11/2020 23:44, Thomas Rodgers wrote:
> Tested x86_64-pc-linux-gnu, committed.

...and there are multiple definition complaints from the linker because 
of two missing "include":

> index 7b2682a577e..23ab2018ca8 100644
> --- a/libstdc++-v3/include/bits/atomic_wait.h
> +++ b/libstdc++-v3/include/bits/atomic_wait.h
> @@ -223,7 +223,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        { _M_w._M_do_wait(_M_version); }
>      };
>  
> -    void
> +    inline void
>      __thread_relax() noexcept
>      {
>  #if defined __i386__ || defined __x86_64__
> @@ -233,7 +233,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>  #endif
>      }
>  
> -    void
> +    inline void
>      __thread_yield() noexcept
>     {
>  #if defined _GLIBCXX_USE_SCHED_YIELD