[modules] Add tests for empty imports.

test/mjsunit/modules-empty-import1.js

Index: test/mjsunit/modules-empty-import1.js
diff --git a/test/mjsunit/modules-circular-valid.js b/test/mjsunit/modules-empty-import1.js
similarity index 59%
copy from test/mjsunit/modules-circular-valid.js
copy to test/mjsunit/modules-empty-import1.js
index e381eefdbc8242c0a6acd38fe7ac05e1d45d6130..60498f187aa5218efbbc0ba5b243366af094d183 100644
--- a/test/mjsunit/modules-circular-valid.js
+++ b/test/mjsunit/modules-empty-import1.js
@@ -4,4 +4,6 @@
 //
 // MODULE
 
-export {a as b} from "modules-skip-circular-valid.js";
+import "modules-skip-empty-import.js";
+import {counter} from "modules-skip-empty-import-aux.js";
+assertEquals(1, counter);