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_syswm.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2021 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
@@ -98,6 +98,10 @@ typedef struct _UIViewController UIViewController;
 typedef Uint32 GLuint;
 #endif
 
+#if defined(SDL_VIDEO_VULKAN) || defined(SDL_VIDEO_METAL)
+#define SDL_METALVIEW_TAG 255
+#endif
+
 #if defined(SDL_VIDEO_DRIVER_ANDROID)
 typedef struct ANativeWindow ANativeWindow;
 typedef void *EGLSurface;
@@ -143,7 +147,8 @@ typedef enum
     SDL_SYSWM_VIVANTE,
     SDL_SYSWM_OS2,
     SDL_SYSWM_HAIKU,
-    SDL_SYSWM_KMSDRM
+    SDL_SYSWM_KMSDRM,
+    SDL_SYSWM_RISCOS
 } SDL_SYSWM_TYPE;
 
 /**
@@ -292,6 +297,9 @@ struct SDL_SysWMinfo
             void *shell_surface;                    /**< DEPRECATED Wayland shell_surface (window manager handle) */
             struct wl_egl_window *egl_window;       /**< Wayland EGL window (native window) */
             struct xdg_surface *xdg_surface;        /**< Wayland xdg surface (window manager handle) */
+            struct xdg_toplevel *xdg_toplevel;      /**< Wayland xdg toplevel role */
+            struct xdg_popup *xdg_popup;            /**< Wayland xdg popup role */
+            struct xdg_positioner *xdg_positioner;  /**< Wayland xdg positioner, for popup */
         } wl;
 #endif
 #if defined(SDL_VIDEO_DRIVER_MIR)  /* no longer available, left for API/ABI compatibility. Remove in 2.1! */