Update SDL2 to newest version to fix 7.1 playback

This fixes 7.1 playback. Before this commit, SDL used 7.1 front audio configuration with Center Left and Center Right speakers, but without Rear speakers.

See https://github.com/libsdl-org/SDL/issues/11709 for more details.

libs/SDL2/include/SDL_cpuinfo.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2024 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
@@ -19,10 +19,16 @@
   3. This notice may not be removed or altered from any source distribution.
 */
 
+/* WIKI CATEGORY: CPUInfo */
+
 /**
- *  \file SDL_cpuinfo.h
+ * # CategoryCPUInfo
  *
- *  CPU feature detection for SDL.
+ * CPU feature detection for SDL.
+ *
+ * These functions are largely concerned with reporting if the system has
+ * access to various SIMD instruction sets, but also has other important info
+ * to share, such as number of logical CPU cores.
  */
 
 #ifndef SDL_cpuinfo_h_
@@ -53,9 +59,11 @@ _m_prefetch(void *__P)
 #ifndef __MMX__
 #define __MMX__
 #endif
+/*
 #ifndef __3dNOW__
 #define __3dNOW__
 #endif
+*/
 #endif
 #ifndef __SSE__
 #define __SSE__