VMS: Compensate for compiler type incompatibility

VMS: Compensate for compiler type incompatibility

The compiler says that 'unsigned long long' isn't the same as
'unsigned __int64'.  Sure, and considering that crypto/rand/rand_vms.c
is specific VMS only code, it's easy to just change the type to the
exact same as what's specified in the system headers.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15613)