Fix pointer size issues on VMS

On VMS, the C compiler can work with 32-bit and 64-bit pointers, and
the command line determines what the initial pointer size shall be.

However, there is some functionality that only works with 32-bit
pointers.  In this case, it's gethostbyname(), getservbyname() and
accompanying structures, so we need to make sure that we define our
own pointers as 32-bit ones.

Furthermore, there seems to be a bug in VMS C netdb.h, where struct
addrinfo is always defined with 32-bit pointers no matter what, but
the functions handling it are adapted to the initial pointer size.
This leads to pointer size warnings when compiling with
/POINTER_SIZE=64.  The workaround is to force struct addrinfo to be
the 64-bit variant if the initial pointer size is 64.

Reviewed-by: Andy Polyakov <appro@openssl.org>