Asio needs to respect OPENSSL_NO_ENGINE preprocessor

[calebmei@…]

OpenSSL on some platform might have open SSL with preprocessor OPENSSL_NO_ENGINE. Specifically this is for Android.

In such event, in

boost/asio/ssl/detail/openssl_types.hpp

should not include,

#include <openssl/engine.h>

And have to provide a default implementation for,

static void ENGINE_cleanup(void) {};

So that boost asio can call this function later on.

Here's the fix I did, please let me know if I should commit it back to the latest boost community.

[chris_kohlhoff]

Fix applied to trunk in changeset [78663]. Applied to release branch in changeset [78708].