Let's look on the code:

menu.c:
int menu_handle_event( Menu *menu, SDL_Event *event )
{
  if ( event )
    switch ( event->type ) {
      case SDL_KEYDOWN:
        switch ( event->key.keysym.sym ) {
          case SDLK_RIGHT:
          [...]
          case SDLK_LEFT:
        }
      }
    }
  }
}

Now, look into SDL header files:

SDL/SDL_events.h:
typedef union SDL_Event {
    Uint8 type;
    SDL_ActiveEvent active;
    SDL_KeyboardEvent key;
    SDL_MouseMotionEvent motion;
    SDL_MouseButtonEvent button;
    SDL_JoyAxisEvent jaxis;
    SDL_JoyBallEvent jball;
    SDL_JoyHatEvent jhat;
    SDL_JoyButtonEvent jbutton;
    SDL_ResizeEvent resize;
    SDL_ExposeEvent expose;
    SDL_QuitEvent quit;
    SDL_UserEvent user;
    SDL_SysWMEvent syswm;
} SDL_Event;

typedef struct SDL_KeyboardEvent {
    Uint8 type; /**< SDL_KEYDOWN or SDL_KEYUP */
    Uint8 which;    /**< The keyboard device index */
    Uint8 state;    /**< SDL_PRESSED or SDL_RELEASED */
    SDL_keysym keysym;
} SDL_KeyboardEvent;

SDL/SDL_keyboard.h:
typedef struct SDL_keysym {
    Uint8 scancode;         /**< hardware specific scancode */
    SDLKey sym;         /**< SDL virtual keysym */
    SDLMod mod;         /**< current key modifiers */
    Uint16 unicode;         /**< translated character */
} SDL_keysym;

SDL/SDL_keysym.h:
typedef enum {
  [...]
  SDLK_RIGHT      = 275,
  SDLK_LEFT       = 276,
  [...]
}

As you can see, the event->key.keysym.sym variable is type of enum. The SDLK_LEFT (276) fits into enum type as SDLK_RIGTH either (int type must fit into enum by C standard.)

Thus there is no problem from point of view of SDL. (Be ware the SDL_Event is union, big enough to contain any of its members.)

However the compilation failed on SDLK_LEFT and passed SDL_RIGHT before. I guess there is some strange redefinition. But I cannot find it.

However the compilation error is due to unbalanced ifdef:

                    case SDLK_RIGHT:
                        if ( !menu->cur_item ) break;
                        item_used = 1;
                        /* callback */
                        callback = menu->cur_item->callback;
                        /* action */
                        switch ( menu->cur_item->type ) {
                            case ITEM_SWITCH:
                            case ITEM_SWITCH_X:
                            case ITEM_RANGE:
                                value_inc( menu->cur_item->value );
                                break;
                            default: item_used = 0; break;
                        }
#ifdef AUDIO_ENABLED
                        if ( item_used ) {
                            stk_sound_play( wav_menu_click );
#endif
                            if ( callback ) (callback)();
                        }
                        break;

If #ifdef should be placed under `if ( item_used ) {' line. See case SDLK_RETURN: for proper use. The same bug is has SDLK_LEFT case too.

And after that the compiles becomes silent. I guess the warning is just because of bad parsing due to curly brackets.

Created attachment 440359 [details]
Move ENABLE_MACRO in menu.c to proper place

This patch fixes lbreakout2 code.

Fix sent to lbreakout2 maintainer via e-mail.

Just a notice about packaging: This game is packaged under name `lbrickbuster2' due to trademark in Fedora.

(In reply to comment #3)
> Created attachment 440359 [details]
> Move ENABLE_MACRO in menu.c to proper place
> 
> This patch fixes lbreakout2 code.

Very clever debugging; I wish I had found it.  Thanks for the patch and also for Comment 7, about packaging.