Fix SDL_LEAN_AND_MEAN logic

[Lzard]

Currently, config flag macros depending on SDL_LEAN_AND_MEAN are always defined, regardless of its value, and only their definedness is checked, not their own values. Those changes fixes this.

See 387774a
Fixes #11344

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While looking for other issues similar to this, I noticed:

• Some config flag macros are conditionally defined, but may still not be true, e.g.:

  SDL/include/SDL3/SDL_platform_defines.h

  Lines 363 to 374 in 8026866

  	#if HAVE_WINAPIFAMILY_H
  	#include <winapifamily.h>
  	#define WINAPI_FAMILY_WINRT (!WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP) && WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP))
  	#else
  	#define WINAPI_FAMILY_WINRT 0
  	#endif /* HAVE_WINAPIFAMILY_H */
  	#if HAVE_WINAPIFAMILY_H && HAVE_WINAPIFAMILY_H
  	#define SDL_WINAPI_FAMILY_PHONE (WINAPI_FAMILY == WINAPI_FAMILY_PHONE_APP)
  	#else
  	#define SDL_WINAPI_FAMILY_PHONE 0
  	#endif

• Third-parties sometimes always define the config flag, but either as true or false, e.g. the OpenGL/Vulkan headers, or even compiler flags:

  SDL/include/SDL3/SDL_platform_defines.h

  Lines 165 to 186 in 8026866

  	/* Fix building with older SDKs that don't define these
  	See this for more information:
  	https://stackoverflow.com/questions/12132933/preprocessor-macro-for-os-x-targets
  	*/
  	#ifndef TARGET_OS_MACCATALYST
  	#define TARGET_OS_MACCATALYST 0
  	#endif
  	#ifndef TARGET_OS_IOS
  	#define TARGET_OS_IOS 0
  	#endif
  	#ifndef TARGET_OS_IPHONE
  	#define TARGET_OS_IPHONE 0
  	#endif
  	#ifndef TARGET_OS_TV
  	#define TARGET_OS_TV 0
  	#endif
  	#ifndef TARGET_OS_SIMULATOR
  	#define TARGET_OS_SIMULATOR 0
  	#endif
  	#ifndef TARGET_OS_VISION
  	#define TARGET_OS_VISION 0
  	#endif

It might be better to always check that config flag macros are defined and true.