[cpp-threads] Asynchronous Execution Issues

[Peter Dimov]

Anthony Williams:
> 1) Make it undefined behaviour for a thread_local destructor to access 
> any objects of static storage duration.

Note that this is basically the case under POSIX, where static destructors 
(or atexit handlers, if one prefers a C-only formulation) run before TLS 
destructors for the thread calling exit() (and, potentially, for all threads 
canceled/told to exit by a static destructor.)