VMS: Adjust the engines directory by adding the pointer size to its name

With OpenSSL 1.1 and on, the engines are tightly tied to the shared
library they're to be used with.  That makes them depend on the
pointer size as well as the shared library version, and this gets
reflected in the name of the directory they're installed in.

Reviewed-by: Rich Salz <rsalz@openssl.org>