backend: Use simple DFS during closure building.

Now closure builder can contain includes. Includes
are another builders which closures must be added
to the building one.
Includes are:

For function closure:
	call targets (including constructors)
	callable reference targets

For class:
	all children declarations
	call targets (including constructors)
        callable reference targets

For constructor:
	call and callable reference targets
	delegating constructor call target
	constructing class closure

backend.native/tests/codegen/function/localFunction2.kt

@@ -0,0 +1,16 @@
+fun main(args: Array<String>) {
+    var a = 0
+    fun local() {
+        class A {
+            val b = 0
+            fun f() {
+                a = b
+            }
+
+        }
+        fun local2() : A {
+            return A()
+        }
+    }
+    println("OK")
+}