Rename directory for back-end tests

compiler/testData/codegen/box/functions/tailRecursion/defaultArgs.kt

@@ -0,0 +1,13 @@
+tailRecursive fun test(x : Int = 0, e : Any = "a") {
+    if (!e.equals("a")) {
+        throw IllegalArgumentException()
+    }
+    if (x > 0) {
+        test(x - 1)
+    }
+}
+
+fun box() : String {
+    test(100000)
+    return "OK"
+}