Handle unused imported functions

test/tests/unused-import/asc.ts

@@ -0,0 +1,5 @@
+declare function other(): void;
+
+export function thing(): i8 {
+  return -1;
+}

test/tests/unused-import/test.js

@@ -0,0 +1,6 @@
+describe("as-bind", function() {
+  it("should handle unused imported functions gracefully", async function() {
+    const instance = await AsBind.instantiate(this.rawModule);
+    assert(instance.exports.thing() === -1);
+  });
+});

transform.js

@@ -86,6 +86,11 @@ class AsBindTransform extends Transform {
     const typeIds = {};
     const importedFunctions = {};
     for (let importedFunction of flatImportedFunctions) {
+      // An imported function with no instances is an unused imported function.
+      // Skip it.
+      if (!importedFunction.instances) {
+        continue;
+      }
       if (
         importedFunction.instances.size > 1 ||
         !importedFunction.instances.has("")