(defn build [list-1 list-2]
  (when-let [[x & xs] list-1]
    (concat (map #(list x %) list-2)
            (build xs list-2))))

(defn build [list-1 list-2]
  (loop [result (list)
         [x & xs] list-1]
    (if x
      (recur (concat result (map #(list x %) list-2)) xs)
      result)))