Use 'JVM_TARGET: 1.8' directive in codegen tests on 1.8 target

compiler/testData/codegen/java8/box/jvm8/diamond.kt

@@ -1,6 +1,7 @@
-// KOTLIN_CONFIGURATION_FLAGS: +JVM.JVM_8_TARGET
+// JVM_TARGET: 1.8
 // WITH_REFLECT
 // FULL_JDK
+
 interface Test {
     fun test(): String {
         return "Test"
@@ -30,6 +31,7 @@ class TestClass2 : TestClass(), Test3 {
 fun box(): String {
     val test = TestClass2().test()
     if (test != "Test2") return "fail 1: $test"
+    // TODO: enable this test once the required behavior is specified
 //    checkNoMethod(TestClass::class.java, "test")
 //    checkNoMethod(Test3::class.java, "test")
 //    checkNoMethod(TestClass2::class.java, "test")
@@ -44,5 +46,5 @@ fun checkNoMethod(clazz: Class<*>, name: String) {
     catch (e: NoSuchMethodException) {
         return
     }
-    throw java.lang.AssertionError("fail " + clazz)
-}
+    throw AssertionError("fail " + clazz)
+}