Fix compile error on C4

MiniEngine.cpp

@@ -86,6 +86,9 @@ namespace MiniEngine
                 return SDL_WINDOW_ALLOW_HIGHDPI;
             case WindowType::MouseCapture:
                 return SDL_WINDOW_MOUSE_CAPTURE;
+
+            /// The following value are not defined on C4.
+            #ifndef __C4DROID__
             case WindowType::AlwaysOnTop:
                 return SDL_WINDOW_ALWAYS_ON_TOP;
             case WindowType::SkipTaskBar:
@@ -96,6 +99,8 @@ namespace MiniEngine
                 return SDL_WINDOW_TOOLTIP;
             case WindowType::PopUpMenu:
                 return SDL_WINDOW_POPUP_MENU;
+            #endif // __C4DROID__
+
             default:
                 return 0;/// Return 0 on default.
             }

MiniEngine_Android.cpp

@@ -7,12 +7,12 @@ namespace MiniEngine
 #if defined(__ANDROID__) && __ANDROID__
 std::string SDLSystem::Android::GetInternal()
 {
-    return string(SDL_AndroidGetInternalStoragePath());
+    return std::string(SDL_AndroidGetInternalStoragePath());
 }
 
 std::string SDLSystem::Android::GetExternal()
 {
-    return string(SDL_AndroidGetExternalStoragePath());
+    return std::string(SDL_AndroidGetExternalStoragePath());
 }
 
 bool SDLSystem::Android::CanReadExternal()

MiniEngine_SQLite.h

@@ -2,6 +2,7 @@
 #include "sqlite/sqlite3.h"
 #include <string>
 #include <memory>
+#include <functional>
 
 namespace MiniEngine
 {