autotools, cmake, macOS: Do not use the system iconv() by default

backport from PR #9676 by @flibitijibibo

CMakeLists.txt

@@ -242,7 +242,7 @@ endif()
 if(UNIX OR MINGW OR MSYS OR (USE_CLANG AND NOT WINDOWS) OR VITA OR PSP OR PS2 OR N3DS)
   set(OPT_DEF_LIBC ON)
 endif()
-if(WINDOWS OR IOS OR TVOS)
+if(WINDOWS OR DARWIN OR MACOSX OR IOS OR TVOS)
   set(SDL_SYSTEM_ICONV_DEFAULT OFF)
 else()
   set(SDL_SYSTEM_ICONV_DEFAULT ON)