BC native tests port to Konan's TestRunner

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

@@ -1,3 +1,7 @@
+package codegen.basics.safe_cast
+
+import kotlin.test.*
+
 open class A
 class B : A()
 class C
@@ -14,8 +18,8 @@ fun safe_cast_negative(): Boolean {
   return foo(c) == null
 }
 
-
-fun main(args: Array<String>) {
+@Test
+fun runTest() {
   val safeCastPositive = safe_cast_positive().toString()
   val safeCastNegative = safe_cast_negative().toString()
   println("safe_cast_positive: " + safeCastPositive)