We need to include the initialisation and construction functions in all
backend, so we include this header when building against SecureTransport
and WinHTTP as well.
This unfortunately isn't as stackable as could be possible, as it
hard-codes the socket stream. This is because the method of using a
custom openssl BIO is not clear, and we do not need this for now. We can
still bring this in if and as we need it.