This doesn't cause trouble with GCC/Clang and libstdc++, but IAR
and its stdlib apparently doesn't compile when you use `fno-exceptions`
and `std::current_exception`/`std::rethrow_exception`.
Fixes#1462
This means
* Adding new configuration toggle `CATCH_CONFIG_DISABLE_EXCEPTIONS`
and a best-guess configuration auto-checking for it.
* Adding new set of internal macros, `CATCH_TRY`, `CATCH_CATCH_ALL`
and `CATCH_CATCH_ANON` that can be used in place of regular `try`,
`catch(...)` and `catch(T const&)` respectively, while disappearing
when `CATCH_CONFIG_DISABLE_EXCEPTIONS` is enabled.
* Replacing all uses of `throw` with calls to `Catch::throw_exception`
customization point.
* Providing a default implementation for the above customization point
when `CATCH_CONFIG_DISABLE_EXCEPTIONS` is set.
* Letting users override this implementation with their own.
* Some minor changes and ifdefs all around to support the above
This works around a bug in libcxxrt handling of active exception count
that caused std::uncaught_exception() to return true even if there was
none.
Closes#1028
Martin Hořeňovský