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_messagebox.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
@@ -32,9 +32,11 @@ extern "C" {
 #endif
 
 /**
- * SDL_MessageBox flags. If supported will display warning icon, etc.
+ * SDL_MessageBox flags.
+ *
+ * If supported will display warning icon, etc.
  */
-typedef enum
+typedef enum SDL_MessageBoxFlags
 {
     SDL_MESSAGEBOX_ERROR                 = 0x00000010,   /**< error dialog */
     SDL_MESSAGEBOX_WARNING               = 0x00000020,   /**< warning dialog */
@@ -46,7 +48,7 @@ typedef enum
 /**
  * Flags for SDL_MessageBoxButtonData.
  */
-typedef enum
+typedef enum SDL_MessageBoxButtonFlags
 {
     SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT = 0x00000001,  /**< Marks the default button when return is hit */
     SDL_MESSAGEBOX_BUTTON_ESCAPEKEY_DEFAULT = 0x00000002   /**< Marks the default button when escape is hit */
@@ -55,9 +57,9 @@ typedef enum
 /**
  * Individual button data.
  */
-typedef struct
+typedef struct SDL_MessageBoxButtonData
 {
-    Uint32 flags;       /**< ::SDL_MessageBoxButtonFlags */
+    Uint32 flags;       /**< SDL_MessageBoxButtonFlags */
     int buttonid;       /**< User defined button id (value returned via SDL_ShowMessageBox) */
     const char * text;  /**< The UTF-8 button text */
 } SDL_MessageBoxButtonData;
@@ -65,12 +67,12 @@ typedef struct
 /**
  * RGB value used in a message box color scheme
  */
-typedef struct
+typedef struct SDL_MessageBoxColor
 {
     Uint8 r, g, b;
 } SDL_MessageBoxColor;
 
-typedef enum
+typedef enum SDL_MessageBoxColorType
 {
     SDL_MESSAGEBOX_COLOR_BACKGROUND,
     SDL_MESSAGEBOX_COLOR_TEXT,
@@ -83,7 +85,7 @@ typedef enum
 /**
  * A set of colors to use for message box dialogs
  */
-typedef struct
+typedef struct SDL_MessageBoxColorScheme
 {
     SDL_MessageBoxColor colors[SDL_MESSAGEBOX_COLOR_MAX];
 } SDL_MessageBoxColorScheme;
@@ -91,9 +93,9 @@ typedef struct
 /**
  * MessageBox structure containing title, text, window, etc.
  */
-typedef struct
+typedef struct SDL_MessageBoxData
 {
-    Uint32 flags;                       /**< ::SDL_MessageBoxFlags */
+    Uint32 flags;                       /**< SDL_MessageBoxFlags */
     SDL_Window *window;                 /**< Parent window, can be NULL */
     const char *title;                  /**< UTF-8 title */
     const char *message;                /**< UTF-8 message text */
@@ -101,7 +103,7 @@ typedef struct
     int numbuttons;
     const SDL_MessageBoxButtonData *buttons;
 
-    const SDL_MessageBoxColorScheme *colorScheme;   /**< ::SDL_MessageBoxColorScheme, can be NULL to use system settings */
+    const SDL_MessageBoxColorScheme *colorScheme;   /**< SDL_MessageBoxColorScheme, can be NULL to use system settings */
 } SDL_MessageBoxData;
 
 /**
@@ -128,8 +130,9 @@ typedef struct
  * to stderr if you can.
  *
  * \param messageboxdata the SDL_MessageBoxData structure with title, text and
- *                       other options
- * \param buttonid the pointer to which user id of hit button should be copied
+ *                       other options.
+ * \param buttonid the pointer to which user id of hit button should be
+ *                 copied.
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *
@@ -168,10 +171,10 @@ extern DECLSPEC int SDLCALL SDL_ShowMessageBox(const SDL_MessageBoxData *message
  * concern, check the return value from this function and fall back to writing
  * to stderr if you can.
  *
- * \param flags an SDL_MessageBoxFlags value
- * \param title UTF-8 title text
- * \param message UTF-8 message text
- * \param window the parent window, or NULL for no parent
+ * \param flags an SDL_MessageBoxFlags value.
+ * \param title UTF-8 title text.
+ * \param message UTF-8 message text.
+ * \param window the parent window, or NULL for no parent.
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *