x11: Avoid including full Vulkan headers.

This dramatically improves compile times of the X11 backend.

Reference Issue #8142.

src/video/x11/SDL_x11video.c

@@ -39,8 +39,6 @@
 #include "SDL_x11opengles.h"
 #endif
 
-#include "SDL_x11vulkan.h"
-
 /* Initialization/Query functions */
 static int X11_VideoInit(SDL_VideoDevice *_this);
 static void X11_VideoQuit(SDL_VideoDevice *_this);

src/video/x11/SDL_x11vulkan.c

@@ -24,6 +24,7 @@
 
 #include "SDL_x11video.h"
 
+#include "../SDL_vulkan_internal.h"
 #include "SDL_x11vulkan.h"
 
 #include <X11/Xlib.h>

src/video/x11/SDL_x11vulkan.h

@@ -23,11 +23,11 @@
 #ifndef SDL_x11vulkan_h_
 #define SDL_x11vulkan_h_
 
-#include "../SDL_vulkan_internal.h"
+#include <SDL3/SDL_vulkan.h>
 
 #if defined(SDL_VIDEO_VULKAN) && defined(SDL_VIDEO_DRIVER_X11)
 
-/*typedef struct xcb_connection_t xcb_connection_t;*/
+typedef struct xcb_connection_t xcb_connection_t;
 typedef xcb_connection_t *(*PFN_XGetXCBConnection)(Display *dpy);
 
 int X11_Vulkan_LoadLibrary(SDL_VideoDevice *_this, const char *path);