[patch] Fix std::notify_all_at_thread_exit test for older glibc

[Jonathan Wakely]

I'm seeing this test timeout on glibc 2.13, which I think is because
it doesn't provide __cxa_atexit_thread_impl and so the thread_local
destructor and the notify_all() happen in an unspecified order.

Tested x86_64-linux, committed to trunk.
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