VMS: pretend to use -znodelete

VMS only unloads shared libraries at process rundown, so tell the
OpenSSL code so by pretending we linked with -znodelete.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1862)
(cherry picked from commit 1186a2b3)