Bugfix: Cleanup some harmless warnings

miner.c

@@ -3607,7 +3607,7 @@ static void restart_threads(void)
 		fd = thr->_work_restart_fd_w;
 		thr->work_restart = true;
 		if (fd != -1)
-			write(fd, "\0", 1);
+			(void)write(fd, "\0", 1);
 	}
 
 	mutex_lock(&restart_lock);
@@ -5619,7 +5619,7 @@ retry_pool:
 
 		struct work *work = make_work();
 		work->pool = pool;
-		const char *rpc_req;
+		char *rpc_req;
 		rpc_req = prepare_rpc_req(work, pool->lp_proto, pool->lp_id);
 		if (!rpc_req)
 			goto lpfail;