VMS: force 'pinshared'

VMS doesn't currently support unloading of shared object, and we need
to reflect that.  Without this, the shlibload test fails

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8131)

(cherry picked from commit d1dd5d6f4c2f13478aa45557b4546febd51f0cb3)