macOS: Do not use the system iconv by default.

macOS 14 changes the iconv implementation which causes things to break, so we may as well match macOS with all the other platforms now.

CMakeLists.txt

@@ -152,7 +152,7 @@ endif()
 # Default option knobs
 set(SDL_LIBC_DEFAULT ON)
 set(SDL_SYSTEM_ICONV_DEFAULT ON)
-if(WINDOWS OR IOS OR TVOS OR VISIONOS OR WATCHOS)
+if(WINDOWS OR MACOS OR IOS OR TVOS OR VISIONOS OR WATCHOS)
   set(SDL_SYSTEM_ICONV_DEFAULT OFF)
 endif()