[Tests] Migrate backend-independent tests from native to compiler/testData.

^KT-65979

compiler/testData/codegen/box/basics/null_check.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+// WITH_STDLIB
+import kotlin.test.*
+
+//--- Test "eqeq" -------------------------------------------------------------//
+
+fun check_eqeq(a: Any?) = a == null
+
+fun null_check_eqeq1() : Boolean {
+  return check_eqeq(Any())
+}
+
+fun null_check_eqeq2() : Boolean {
+  return check_eqeq(null)
+}
+
+//--- Test "eqeqeq" -----------------------------------------------------------//
+
+fun check_eqeqeq(a: Any?) = a === null
+
+fun null_check_eqeqeq1() : Boolean {
+  return check_eqeqeq(Any())
+}
+
+fun null_check_eqeqeq2() : Boolean {
+  return check_eqeqeq(null)
+}
+
+fun box(): String {
+  if (null_check_eqeq1())    return "FAIL null_check_eqeq1()"
+  if (!null_check_eqeq2())   return "FAIL !null_check_eqeq2()"
+  if (null_check_eqeqeq1())  return "FAIL null_check_eqeqeq1()"
+  if (!null_check_eqeqeq2()) return "FAIL !null_check_eqeqeq2()"
+
+  return "OK"
+}