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_config_os2.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
@@ -47,7 +47,7 @@
 /* dynamically loaded libusb-1.0 dll: */
 #define SDL_LIBUSB_DYNAMIC "usb100.dll"
 #endif
-/*#undef SDL_JOYSTICK_VIRTUAL */
+#define SDL_JOYSTICK_VIRTUAL 1
 
 /* Enable OpenGL support */
 /* #undef SDL_VIDEO_OPENGL */
@@ -114,9 +114,6 @@
 #define HAVE_MEMCPY 1
 #define HAVE_MEMMOVE 1
 #define HAVE_MEMCMP 1
-#define HAVE_WCSLEN 1
-#define HAVE_WCSLCPY 1
-#define HAVE_WCSLCAT 1
 #define HAVE_WCSCMP 1
 #define HAVE__WCSICMP 1
 #define HAVE__WCSNICMP 1