CLJS-1737: Self-host: clojure alias implicit macro use regression

When checking for clojure.* -> cljs.* cases in `get-expander-ns`, we
want NS resolution to return nil if it can't resolve either the macros
NS or the NS alias. `resolve-macro-ns-alias` and `resolve-ns-alias` need
to be tweaked to return nil in this case.

src/main/clojure/cljs/analyzer.cljc

@@ -690,13 +690,19 @@
       (fn [env prefix suffix]
         (throw (error env (str "Unable to resolve var: " suffix " in this context")))))))
 
-(defn resolve-ns-alias [env name]
-  (let [sym (symbol name)]
-    (get (:requires (:ns env)) sym sym)))
-
-(defn resolve-macro-ns-alias [env name]
-  (let [sym (symbol name)]
-    (get (:require-macros (:ns env)) sym sym)))
+(defn resolve-ns-alias
+  ([env name]
+   (resolve-ns-alias env name (symbol name)))
+  ([env name default]
+   (let [sym (symbol name)]
+     (get (:requires (:ns env)) sym default))))
+
+(defn resolve-macro-ns-alias
+  ([env name]
+   (resolve-macro-ns-alias env name (symbol name)))
+  ([env name default]
+   (let [sym (symbol name)]
+     (get (:require-macros (:ns env)) sym default))))
 
 (defn confirm-ns
   "Given env, an analysis environment, and ns-sym, a symbol identifying a
@@ -2574,8 +2580,8 @@
 
 (defn get-expander-ns [env ^String nstr]
   ;; first check for clojure.* -> cljs.* cases
-  (let [res  (or (resolve-macro-ns-alias env (symbol nstr))
-                 (resolve-ns-alias env (symbol nstr)))
+  (let [res  (or (resolve-macro-ns-alias env nstr nil)
+                 (resolve-ns-alias env nstr nil))
         nstr (if res (str res) nstr)]
     (cond
      #?@(:clj  [(= "clojure.core" nstr) (find-ns 'cljs.core)]

src/test/cljs/cljs/clojure_alias_test.cljs

@@ -9,3 +9,7 @@
 (deftest aliases-test
   (is? (= spec? clojure.spec/spec? cljs.spec/spec?))
   (is? (foo number?)))
+
+(deftest use-macros
+  (s/def ::even? (s/and number? even?))
+  (is? (s/valid? ::even? 2)))