Fix unused parameter and variable warnings.

src/zmq_utils.cpp

@@ -188,12 +188,13 @@ int zmq_curve_keypair (char *z85_public_key, char *z85_secret_key)
     //  Is there a sensible errno to set here?
     if (rc)
         return rc;
-    
+
     zmq_z85_encode (z85_public_key, public_key, 32);
     zmq_z85_encode (z85_secret_key, secret_key, 32);
-    
+
     return 0;
 #else // requires libsodium
+    (void) z85_public_key, (void) z85_secret_key;
     errno = ENOTSUP;
     return -1;
 #endif