util/mkdef.pl: Make symbol version processing Linux only

For Windows, we care which way it is, the resulting file is just a pile
of symbols.  For VMS, we really need to care about the numeric ordering,
and getting the symbols sorted by symbol version too didn't agree with
that.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3804)