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_blendmode.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
@@ -20,9 +20,9 @@
 */
 
 /**
- *  \file SDL_blendmode.h
+ * # CategoryBlendmode
  *
- *  Header file declaring the SDL_BlendMode enumeration
+ * Header file declaring the SDL_BlendMode enumeration
  */
 
 #ifndef SDL_blendmode_h_
@@ -35,9 +35,9 @@ extern "C" {
 #endif
 
 /**
- *  \brief The blend mode used in SDL_RenderCopy() and drawing operations.
+ * The blend mode used in SDL_RenderCopy() and drawing operations.
  */
-typedef enum
+typedef enum SDL_BlendMode
 {
     SDL_BLENDMODE_NONE = 0x00000000,     /**< no blending
                                               dstRGBA = srcRGBA */
@@ -60,21 +60,22 @@ typedef enum
 } SDL_BlendMode;
 
 /**
- *  \brief The blend operation used when combining source and destination pixel components
+ * The blend operation used when combining source and destination pixel
+ * components
  */
-typedef enum
+typedef enum SDL_BlendOperation
 {
     SDL_BLENDOPERATION_ADD              = 0x1,  /**< dst + src: supported by all renderers */
-    SDL_BLENDOPERATION_SUBTRACT         = 0x2,  /**< dst - src : supported by D3D9, D3D11, OpenGL, OpenGLES */
-    SDL_BLENDOPERATION_REV_SUBTRACT     = 0x3,  /**< src - dst : supported by D3D9, D3D11, OpenGL, OpenGLES */
+    SDL_BLENDOPERATION_SUBTRACT         = 0x2,  /**< src - dst : supported by D3D9, D3D11, OpenGL, OpenGLES */
+    SDL_BLENDOPERATION_REV_SUBTRACT     = 0x3,  /**< dst - src : supported by D3D9, D3D11, OpenGL, OpenGLES */
     SDL_BLENDOPERATION_MINIMUM          = 0x4,  /**< min(dst, src) : supported by D3D9, D3D11 */
     SDL_BLENDOPERATION_MAXIMUM          = 0x5   /**< max(dst, src) : supported by D3D9, D3D11 */
 } SDL_BlendOperation;
 
 /**
- *  \brief The normalized factor used to multiply pixel components
+ * The normalized factor used to multiply pixel components
  */
-typedef enum
+typedef enum SDL_BlendFactor
 {
     SDL_BLENDFACTOR_ZERO                = 0x1,  /**< 0, 0, 0, 0 */
     SDL_BLENDFACTOR_ONE                 = 0x2,  /**< 1, 1, 1, 1 */
@@ -158,18 +159,18 @@ typedef enum
  * case.
  *
  * \param srcColorFactor the SDL_BlendFactor applied to the red, green, and
- *                       blue components of the source pixels
+ *                       blue components of the source pixels.
  * \param dstColorFactor the SDL_BlendFactor applied to the red, green, and
- *                       blue components of the destination pixels
+ *                       blue components of the destination pixels.
  * \param colorOperation the SDL_BlendOperation used to combine the red,
  *                       green, and blue components of the source and
- *                       destination pixels
+ *                       destination pixels.
  * \param srcAlphaFactor the SDL_BlendFactor applied to the alpha component of
- *                       the source pixels
+ *                       the source pixels.
  * \param dstAlphaFactor the SDL_BlendFactor applied to the alpha component of
- *                       the destination pixels
+ *                       the destination pixels.
  * \param alphaOperation the SDL_BlendOperation used to combine the alpha
- *                       component of the source and destination pixels
+ *                       component of the source and destination pixels.
  * \returns an SDL_BlendMode that represents the chosen factors and
  *          operations.
  *