Refactor util/mkdef.pl for clearer separation of functionality

Move the .num updating functionality to util/mknum.pl.
Rewrite util/mkdef.pl to create .def / .map / .opt files exclusively,
using the separate ordinals reading module.
Adapt the build files.
Adapt the symbol presence test.

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7191)