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_shape.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2018 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
@@ -44,33 +44,38 @@ extern "C" {
 #define SDL_WINDOW_LACKS_SHAPE -3
 
 /**
- *  \brief Create a window that can be shaped with the specified position, dimensions, and flags.
+ * Create a window that can be shaped with the specified position, dimensions,
+ * and flags.
  *
- *  \param title The title of the window, in UTF-8 encoding.
- *  \param x     The x position of the window, ::SDL_WINDOWPOS_CENTERED, or
- *               ::SDL_WINDOWPOS_UNDEFINED.
- *  \param y     The y position of the window, ::SDL_WINDOWPOS_CENTERED, or
- *               ::SDL_WINDOWPOS_UNDEFINED.
- *  \param w     The width of the window.
- *  \param h     The height of the window.
- *  \param flags The flags for the window, a mask of SDL_WINDOW_BORDERLESS with any of the following:
- *               ::SDL_WINDOW_OPENGL,     ::SDL_WINDOW_INPUT_GRABBED,
- *               ::SDL_WINDOW_HIDDEN,     ::SDL_WINDOW_RESIZABLE,
- *               ::SDL_WINDOW_MAXIMIZED,  ::SDL_WINDOW_MINIMIZED,
- *       ::SDL_WINDOW_BORDERLESS is always set, and ::SDL_WINDOW_FULLSCREEN is always unset.
+ * \param title The title of the window, in UTF-8 encoding.
+ * \param x The x position of the window, ::SDL_WINDOWPOS_CENTERED, or
+ *          ::SDL_WINDOWPOS_UNDEFINED.
+ * \param y The y position of the window, ::SDL_WINDOWPOS_CENTERED, or
+ *          ::SDL_WINDOWPOS_UNDEFINED.
+ * \param w The width of the window.
+ * \param h The height of the window.
+ * \param flags The flags for the window, a mask of SDL_WINDOW_BORDERLESS with
+ *              any of the following: ::SDL_WINDOW_OPENGL,
+ *              ::SDL_WINDOW_INPUT_GRABBED, ::SDL_WINDOW_HIDDEN,
+ *              ::SDL_WINDOW_RESIZABLE, ::SDL_WINDOW_MAXIMIZED,
+ *              ::SDL_WINDOW_MINIMIZED, ::SDL_WINDOW_BORDERLESS is always set,
+ *              and ::SDL_WINDOW_FULLSCREEN is always unset.
+ * \return the window created, or NULL if window creation failed.
  *
- *  \return The window created, or NULL if window creation failed.
+ * \since This function is available since SDL 2.0.0.
  *
- *  \sa SDL_DestroyWindow()
+ * \sa SDL_DestroyWindow
  */
 extern DECLSPEC SDL_Window * SDLCALL SDL_CreateShapedWindow(const char *title,unsigned int x,unsigned int y,unsigned int w,unsigned int h,Uint32 flags);
 
 /**
- * \brief Return whether the given window is a shaped window.
+ * Return whether the given window is a shaped window.
  *
  * \param window The window to query for being shaped.
+ * \return SDL_TRUE if the window is a window that can be shaped, SDL_FALSE if
+ *         the window is unshaped or NULL.
  *
- * \return SDL_TRUE if the window is a window that can be shaped, SDL_FALSE if the window is unshaped or NULL.
+ * \since This function is available since SDL 2.0.0.
  *
  * \sa SDL_CreateShapedWindow
  */
@@ -106,29 +111,35 @@ typedef struct SDL_WindowShapeMode {
 } SDL_WindowShapeMode;
 
 /**
- * \brief Set the shape and parameters of a shaped window.
+ * Set the shape and parameters of a shaped window.
  *
  * \param window The shaped window whose parameters should be set.
  * \param shape A surface encoding the desired shape for the window.
  * \param shape_mode The parameters to set for the shaped window.
+ * \return 0 on success, SDL_INVALID_SHAPE_ARGUMENT on an invalid shape
+ *         argument, or SDL_NONSHAPEABLE_WINDOW if the SDL_Window given does
+ *         not reference a valid shaped window.
  *
- * \return 0 on success, SDL_INVALID_SHAPE_ARGUMENT on an invalid shape argument, or SDL_NONSHAPEABLE_WINDOW
- *           if the SDL_Window given does not reference a valid shaped window.
+ * \since This function is available since SDL 2.0.0.
  *
  * \sa SDL_WindowShapeMode
- * \sa SDL_GetShapedWindowMode.
+ * \sa SDL_GetShapedWindowMode
  */
 extern DECLSPEC int SDLCALL SDL_SetWindowShape(SDL_Window *window,SDL_Surface *shape,SDL_WindowShapeMode *shape_mode);
 
 /**
- * \brief Get the shape parameters of a shaped window.
+ * Get the shape parameters of a shaped window.
  *
  * \param window The shaped window whose parameters should be retrieved.
- * \param shape_mode An empty shape-mode structure to fill, or NULL to check whether the window has a shape.
+ * \param shape_mode An empty shape-mode structure to fill, or NULL to check
+ *                   whether the window has a shape.
+ * \return 0 if the window has a shape and, provided shape_mode was not NULL,
+ *         shape_mode has been filled with the mode data,
+ *         SDL_NONSHAPEABLE_WINDOW if the SDL_Window given is not a shaped
+ *         window, or SDL_WINDOW_LACKS_SHAPE if the SDL_Window given is a
+ *         shapeable window currently lacking a shape.
  *
- * \return 0 if the window has a shape and, provided shape_mode was not NULL, shape_mode has been filled with the mode
- *           data, SDL_NONSHAPEABLE_WINDOW if the SDL_Window given is not a shaped window, or SDL_WINDOW_LACKS_SHAPE if
- *           the SDL_Window given is a shapeable window currently lacking a shape.
+ * \since This function is available since SDL 2.0.0.
  *
  * \sa SDL_WindowShapeMode
  * \sa SDL_SetWindowShape