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

backport from PR #9676 by @flibitijibibo

configure

@@ -18816,7 +18816,7 @@ fi
 
 enable_system_iconv_default=yes
 case "$host" in
-  *-*-cygwin*|*-*-mingw*)
+  *-*-cygwin*|*-*-mingw*|*-*-darwin*|*-ios-*)
     enable_system_iconv_default=no
     ;;
 esac