Support native top-level functions

compiler/testData/codegen/boxWithStdlib/native/default.kt

@@ -9,6 +9,8 @@ object ObjWithNative {
     platformStatic native fun bar(l: Long, s: String = ""): Double
 }
 
+native fun topLevel(x: Int = 1): Double
+
 fun box(): String {
     var d = 0.0
 
@@ -27,5 +29,13 @@ fun box(): String {
     catch (e: java.lang.UnsatisfiedLinkError) {
         if (e.getMessage() != "foo.ObjWithNative.foo(I)D") return "Fail 2: " + e.getMessage()
     }
+
+    try {
+        d = topLevel()
+        return "Link error expected on object"
+    }
+    catch (e: java.lang.UnsatisfiedLinkError) {
+        if (e.getMessage() != "foo.FooPackage.topLevel(I)D") return "Fail 3: " + e.getMessage()
+    }
     return "OK"
 }