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_platform.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
@@ -65,11 +65,15 @@
 #undef __LINUX__ /* do we need to do this? */
 #define __ANDROID__ 1
 #endif
+#if defined(__NGAGE__)
+#undef __NGAGE__
+#define __NGAGE__ 1
+#endif
 
 #if defined(__APPLE__)
 /* lets us know what version of Mac OS X we're compiling on */
-#include "AvailabilityMacros.h"
-#include "TargetConditionals.h"
+#include <AvailabilityMacros.h>
+#include <TargetConditionals.h>
 
 /* Fix building with older SDKs that don't define these
    See this for more information:
@@ -104,9 +108,9 @@
 /* if not compiling for iOS */
 #undef __MACOSX__
 #define __MACOSX__  1
-#if MAC_OS_X_VERSION_MIN_REQUIRED < 1060
-# error SDL for Mac OS X only supports deploying on 10.6 and above.
-#endif /* MAC_OS_X_VERSION_MIN_REQUIRED < 1060 */
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 1070
+# error SDL for Mac OS X only supports deploying on 10.7 and above.
+#endif /* MAC_OS_X_VERSION_MIN_REQUIRED < 1070 */
 #endif /* TARGET_OS_IPHONE */
 #endif /* defined(__APPLE__) */
 
@@ -140,7 +144,7 @@
 #endif
 
 #if defined(WIN32) || defined(_WIN32) || defined(__CYGWIN__) || defined(__MINGW32__)
-/* Try to find out if we're compiling for WinRT or non-WinRT */
+/* Try to find out if we're compiling for WinRT, GDK or non-WinRT/GDK */
 #if defined(_MSC_VER) && defined(__has_include)
 #if __has_include(<winapifamily.h>)
 #define HAVE_WINAPIFAMILY_H 1
@@ -165,6 +169,15 @@
 #if WINAPI_FAMILY_WINRT
 #undef __WINRT__
 #define __WINRT__ 1
+#elif defined(_GAMING_DESKTOP) /* GDK project configuration always defines _GAMING_XXX */
+#undef __WINGDK__
+#define __WINGDK__ 1
+#elif defined(_GAMING_XBOX_XBOXONE)
+#undef __XBOXONE__
+#define __XBOXONE__ 1
+#elif defined(_GAMING_XBOX_SCARLETT)
+#undef __XBOXSERIES__
+#define __XBOXSERIES__ 1
 #else
 #undef __WINDOWS__
 #define __WINDOWS__ 1
@@ -175,10 +188,18 @@
 #undef __WIN32__
 #define __WIN32__ 1
 #endif
+/* This is to support generic "any GDK" separate from a platform-specific GDK */
+#if defined(__WINGDK__) || defined(__XBOXONE__) || defined(__XBOXSERIES__)
+#undef __GDK__
+#define __GDK__ 1
+#endif
 #if defined(__PSP__)
 #undef __PSP__
 #define __PSP__ 1
 #endif
+#if defined(PS2)
+#define __PS2__ 1
+#endif
 
 /* The NACL compiler defines __native_client__ and __pnacl__
  * Ref: http://www.chromium.org/nativeclient/pnacl/stability-of-the-pnacl-bitcode-abi
@@ -219,6 +240,8 @@ extern "C" {
  *
  * \returns the name of the platform. If the correct platform name is not
  *          available, returns a string beginning with the text "Unknown".
+ *
+ * \since This function is available since SDL 2.0.0.
  */
 extern DECLSPEC const char * SDLCALL SDL_GetPlatform (void);