Enable printf format argument checking.

The original attempt missed the fact that Print is a member function,
so the first argument is the implicit 'this'.

Change-Id: I963b668c5432804c767f0a2e3ef7dea5978a1218
diff --git a/screen_ui.h b/screen_ui.h
index 210fd3e..82647ac 100644
--- a/screen_ui.h
+++ b/screen_ui.h
@@ -47,11 +47,11 @@
     bool WasTextEverVisible();
 
     // printing messages
-    void Print(const char* fmt, ...); // __attribute__((format(printf, 1, 2)));
+    void Print(const char* fmt, ...) __printflike(2, 3);
 
     // menu display
     void StartMenu(const char* const * headers, const char* const * items,
-                           int initial_selection);
+                   int initial_selection);
     int SelectMenu(int sel);
     void EndMenu();