SDL: SDL_camera_v4l2.c: fix build against old kernel headers.

SDL Commits
1 
From 616c21d7309a933c7f115c0aabd5af7d0e78fa36 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Thu, 6 Nov 2025 18:28:50 +0300
Subject: [PATCH] SDL_camera_v4l2.c: fix build against old kernel headers.

---
 src/camera/v4l2/SDL_camera_v4l2.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/camera/v4l2/SDL_camera_v4l2.c b/src/camera/v4l2/SDL_camera_v4l2.c
index 86ea3f74ca5aa..fe2491b61952e 100644
--- a/src/camera/v4l2/SDL_camera_v4l2.c
+++ b/src/camera/v4l2/SDL_camera_v4l2.c
@@ -32,6 +32,9 @@
 #include <unistd.h>
 #include <linux/videodev2.h>
 
+#ifndef V4L2_PIX_FMT_RGBX32
+#define V4L2_PIX_FMT_RGBX32 v4l2_fourcc('X','B','2','4')
+#endif
 #ifndef V4L2_CAP_DEVICE_CAPS
 // device_caps was added to struct v4l2_capability as of kernel 3.4.
 #define device_caps reserved[0]