This may need more work to prevent warning messages during
"make cleandir" when the commands in "!=" assignments are executed
even though tools may not have been built.
Big5-2003, Big5-ETen, Big5-IBM, Big-5E, Big-5+.
``Big5 is now the alias of Big5-ETen,
if you want Unicode.org's obsolete mappings, use Big5-IBM instead.