Update source to SDL2 2.0.12

Edward Rudd

2020-05-02 03f8528315fa46c95991a34f3325d7b33ae5538c

 source/src/video/wayland/SDL_waylandvulkan.h

@@ -1,6 +1,6 @@
/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2018 Sam Lantinga <slouken@libsdl.org>
  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
@@ -40,6 +40,7 @@
                                          SDL_Window *window,
                                          unsigned *count,
                                          const char **names);
void Wayland_Vulkan_GetDrawableSize(_THIS, SDL_Window *window, int *w, int *h);
SDL_bool Wayland_Vulkan_CreateSurface(_THIS,
                                  SDL_Window *window,
                                  VkInstance instance,