Don't worry the name is historic it does not us the arc4 cipher any longer, at least on OpenBSD. They switched to chacha20 as stream cipher.
The analog of zx_cprng_draw is getentropy(2): http://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/... except zx_cprng_draw kills the process, while getentropy returns an error.
The analog of zx_cprng_draw is getentropy(2): http://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/... except zx_cprng_draw kills the process, while getentropy returns an error.