P.S. I like the alternative approach defined in https://github.com/panaseleus/stack_unwinding even if the code is not completely portable in C++11.
Yes, it based on top of platform-specific implementation of uncaught_exception_count.
However, I made it work on all platforms I have access to - MSVC, GCC, Clang ( see full list at github readme ).
And I think it should be easy to implement it on other platforms, because info about current exceptions in flight should be stored somewhere.
By the way, at 1:18:10 Andrei mentioned that he would accept GCC only solution.