TEST: tests for safe cast added

backend.native/tests/codegen/basics/safe_cast.kt

@@ -0,0 +1,23 @@
+open class A
+class B : A()
+class C
+
+fun foo(a: Any) : A? = a as? A
+
+fun safe_cast_positive(): Boolean {
+  val b = B()
+  return foo(b) === b
+}
+
+fun safe_cast_negative(): Boolean {
+  val c = C()
+  return foo(c) == null
+}
+
+
+fun main(args: Array<String>) {
+  val safeCastPositive = safe_cast_positive().toString()
+  val safeCastNegative = safe_cast_negative().toString()
+  println("safe_cast_positive: " + safeCastPositive)
+  println("safe_cast_negative: " + safeCastNegative)
+}