LibreSSL uses arc4random for random number generation. The way this has been implemented, i.e. replacing the calls to RAND_bytes and RAND_pseudo_bytes by a call to arc4random, removed the support for a custom RAND engine, because there is no code anymore which calls the functions of the RAND engine provided by ENGINE_set_RAND and ENGINE_set_default(e, ENGINE_METHOD_RAND).

Was the removal of RAND engine support intended?