backend/tests: Add blackbox tests from Kotlin JVM

Added tests from testData/codegen/box directory. There are blackbox tests
in other directories and they are to be added.

backend.native/tests/external/codegen/blackbox/classes/kt2482.kt

@@ -0,0 +1,9 @@
+public fun box() : String {
+    if ( 0 == 0 ) { // Does not crash if either this...
+        if ( 0 == 0 ) { // ...or this is changed to if ( true )
+            // Does not crash if the following is uncommented.
+            //println("foo")
+        }
+    }
+    return "OK"
+}