Update to SDL 2.24.0 and add separate macOS UB2 dylib

Update mingw and macOS SDL libraries to 2.24.0. (MSVC .lib files and
Xcode project haven't been updated.)

There is now a separate SDL dylib for macOS Universal Binary 1 and 2
because SDL 2.24.0 dropped support for macOS 10.6 (which is last to
support x86). Documentation says SDL 2.24.0 also dropped macOS 10.7
and 10.8 too. So UB2 is now 10.9 or later while 10.5 to 10.8 live in
UB1.

Compiled using osxcross with macOS 11.3 SDK. Ran "strip -x" on Windows
and macOS libraries. Ad-hoc signed dylib using PyOxidizer rcodesign to
fix digest checksums after strip.

code/SDL2/include/SDL_main.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2022 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
@@ -51,6 +51,15 @@
 */
 #define SDL_MAIN_NEEDED
 
+#elif defined(__GDK__)
+/* On GDK, SDL provides a main function that initializes the game runtime.
+
+   Please note that #include'ing SDL_main.h is not enough to get a main()
+   function working. You must either link against SDL2main or, if not possible,
+   call the SDL_GDKRunApp function from your entry point.
+*/
+#define SDL_MAIN_NEEDED
+
 #elif defined(__IPHONEOS__)
 /* On iOS SDL provides a main function that creates an application delegate
    and starts the iOS application run loop.
@@ -83,6 +92,22 @@
 */
 #define SDL_MAIN_NEEDED
 
+#elif defined(__PSP__)
+/* On PSP SDL provides a main function that sets the module info,
+   activates the GPU and starts the thread required to be able to exit
+   the software.
+
+   If you provide this yourself, you may define SDL_MAIN_HANDLED
+ */
+#define SDL_MAIN_AVAILABLE
+
+#elif defined(__PS2__)
+#define SDL_MAIN_AVAILABLE
+
+#define SDL_PS2_SKIP_IOP_RESET() \
+   void reset_IOP(); \
+   void reset_IOP() {}
+
 #endif
 #endif /* SDL_MAIN_HANDLED */
 
@@ -122,34 +147,78 @@ extern SDLMAIN_DECLSPEC int SDL_main(int argc, char *argv[]);
 
 
 /**
- *  This is called by the real SDL main function to let the rest of the
- *  library know that initialization was done properly.
+ * Circumvent failure of SDL_Init() when not using SDL_main() as an entry
+ * point.
  *
- *  Calling this yourself without knowing what you're doing can cause
- *  crashes and hard to diagnose problems with your application.
+ * This function is defined in SDL_main.h, along with the preprocessor rule to
+ * redefine main() as SDL_main(). Thus to ensure that your main() function
+ * will not be changed it is necessary to define SDL_MAIN_HANDLED before
+ * including SDL.h.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_Init
  */
 extern DECLSPEC void SDLCALL SDL_SetMainReady(void);
 
-#ifdef __WIN32__
+#if defined(__WIN32__) || defined(__GDK__)
 
 /**
- *  This can be called to set the application class at startup
+ * Register a win32 window class for SDL's use.
+ *
+ * This can be called to set the application window class at startup. It is
+ * safe to call this multiple times, as long as every call is eventually
+ * paired with a call to SDL_UnregisterApp, but a second registration attempt
+ * while a previous registration is still active will be ignored, other than
+ * to increment a counter.
+ *
+ * Most applications do not need to, and should not, call this directly; SDL
+ * will call it when initializing the video subsystem.
+ *
+ * \param name the window class name, in UTF-8 encoding. If NULL, SDL
+ *             currently uses "SDL_app" but this isn't guaranteed.
+ * \param style the value to use in WNDCLASSEX::style. If `name` is NULL, SDL
+ *              currently uses `(CS_BYTEALIGNCLIENT | CS_OWNDC)` regardless of
+ *              what is specified here.
+ * \param hInst the HINSTANCE to use in WNDCLASSEX::hInstance. If zero, SDL
+ *              will use `GetModuleHandle(NULL)` instead.
+ * \returns 0 on success, -1 on error. SDL_GetError() may have details.
+ *
+ * \since This function is available since SDL 2.0.2.
+ */
+extern DECLSPEC int SDLCALL SDL_RegisterApp(const char *name, Uint32 style, void *hInst);
+
+/**
+ * Deregister the win32 window class from an SDL_RegisterApp call.
+ *
+ * This can be called to undo the effects of SDL_RegisterApp.
+ *
+ * Most applications do not need to, and should not, call this directly; SDL
+ * will call it when deinitializing the video subsystem.
+ *
+ * It is safe to call this multiple times, as long as every call is eventually
+ * paired with a prior call to SDL_RegisterApp. The window class will only be
+ * deregistered when the registration counter in SDL_RegisterApp decrements to
+ * zero through calls to this function.
+ *
+ * \since This function is available since SDL 2.0.2.
  */
-extern DECLSPEC int SDLCALL SDL_RegisterApp(char *name, Uint32 style, void *hInst);
 extern DECLSPEC void SDLCALL SDL_UnregisterApp(void);
 
-#endif /* __WIN32__ */
+#endif /* defined(__WIN32__) || defined(__GDK__) */
 
 
 #ifdef __WINRT__
 
 /**
- *  \brief Initializes and launches an SDL/WinRT application.
+ * Initialize and launch an SDL/WinRT application.
  *
- *  \param mainFunction The SDL app's C-style main().
- *  \param reserved Reserved for future use; should be NULL
- *  \return 0 on success, -1 on failure.  On failure, use SDL_GetError to retrieve more
- *      information on the failure.
+ * \param mainFunction the SDL app's C-style main(), an SDL_main_func
+ * \param reserved reserved for future use; should be NULL
+ * \returns 0 on success or -1 on failure; call SDL_GetError() to retrieve
+ *          more information on the failure.
+ *
+ * \since This function is available since SDL 2.0.3.
  */
 extern DECLSPEC int SDLCALL SDL_WinRTRunApp(SDL_main_func mainFunction, void * reserved);
 
@@ -158,17 +227,34 @@ extern DECLSPEC int SDLCALL SDL_WinRTRunApp(SDL_main_func mainFunction, void * r
 #if defined(__IPHONEOS__)
 
 /**
- *  \brief Initializes and launches an SDL application.
+ * Initializes and launches an SDL application.
  *
- *  \param argc The argc parameter from the application's main() function
- *  \param argv The argv parameter from the application's main() function
- *  \param mainFunction The SDL app's C-style main().
- *  \return the return value from mainFunction
+ * \param argc The argc parameter from the application's main() function
+ * \param argv The argv parameter from the application's main() function
+ * \param mainFunction The SDL app's C-style main(), an SDL_main_func
+ * \return the return value from mainFunction
+ *
+ * \since This function is available since SDL 2.0.10.
  */
 extern DECLSPEC int SDLCALL SDL_UIKitRunApp(int argc, char *argv[], SDL_main_func mainFunction);
 
 #endif /* __IPHONEOS__ */
 
+#ifdef __GDK__
+
+/**
+ * Initialize and launch an SDL GDK application.
+ *
+ * \param mainFunction the SDL app's C-style main(), an SDL_main_func
+ * \param reserved reserved for future use; should be NULL
+ * \returns 0 on success or -1 on failure; call SDL_GetError() to retrieve
+ *          more information on the failure.
+ *
+ * \since This function is available since SDL 2.24.0.
+ */
+extern DECLSPEC int SDLCALL SDL_GDKRunApp(SDL_main_func mainFunction, void *reserved);
+
+#endif /* __GDK__ */
 
 #ifdef __cplusplus
 }