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/controlStructures/emptyDoWhile.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    do while (false);
+
+    var x = 0
+    do while (x++<5);
+    if (x != 6) return "Fail: $x"
+
+    return "OK"
+}