Add missing parameters and return types to SDL2 header docs (#13162)

include/SDL_system.h

@@ -463,6 +463,7 @@ extern DECLSPEC int SDLCALL SDL_AndroidShowToast(const char* message, int durati
  *
  * \param command user command that must be greater or equal to 0x8000.
  * \param param user parameter.
+ * \returns 0 on success, otherwise -1.
  *
  * \since This function is available since SDL 2.0.22.
  */