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/begin_code.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
@@ -19,12 +19,12 @@
   3. This notice may not be removed or altered from any source distribution.
 */
 
+/* WIKI CATEGORY: BeginCode */
+
 /**
- *  \file begin_code.h
- *
- *  This file sets things up for C dynamic library function definitions,
- *  static inlined functions, and structures aligned at 4-byte alignment.
- *  If you don't like ugly C preprocessor code, don't look at this file. :)
+ * begin_code.h sets things up for C dynamic library function definitions,
+ * static inlined functions, and structures aligned at 4-byte alignment.
+ * If you don't like ugly C preprocessor code, don't look at this file. :)
  */
 
 /* This shouldn't be nested -- included it around code only. */
@@ -36,6 +36,8 @@
 #ifndef SDL_DEPRECATED
 #  if defined(__GNUC__) && (__GNUC__ >= 4)  /* technically, this arrived in gcc 3.1, but oh well. */
 #    define SDL_DEPRECATED __attribute__((deprecated))
+#  elif defined(_MSC_VER)
+#    define SDL_DEPRECATED __declspec(deprecated)
 #  else
 #    define SDL_DEPRECATED
 #  endif
@@ -170,7 +172,7 @@
     (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202000L)
 #define SDL_FALLTHROUGH [[fallthrough]]
 #else
-#if defined(__has_attribute)
+#if defined(__has_attribute) && !defined(__SUNPRO_C) && !defined(__SUNPRO_CC)
 #define SDL_HAS_FALLTHROUGH __has_attribute(__fallthrough__)
 #else
 #define SDL_HAS_FALLTHROUGH 0