Tests on migrating main thread and memory leaks with interop (#4494)

kotlin-native/backend.native/tests/interop/migrating_main_thread/lib.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+class A {
+    var i = 0
+}
+
+private var globalA = A()
+
+fun writeToA(i: Int) {
+    globalA.i = i
+}
+
+fun readFromA() = globalA.i