backend: add tests for lambda functions

backend.native/tests/codegen/lambda/lambda8.kt

@@ -0,0 +1,24 @@
+fun main(args : Array<String>) {
+    val lambda1 = bar("first")
+    val lambda2 = bar("second")
+
+    lambda1()
+    lambda2()
+    lambda1()
+    lambda2()
+}
+
+fun bar(str: String): () -> Unit {
+    var x = Integer(0)
+
+    return {
+        println(str)
+        println(x.toString())
+        x = x + 1
+    }
+}
+
+class Integer(val value: Int) {
+    override fun toString() = value.toString()
+    operator fun plus(other: Int) = Integer(value + other)
+}