VMS: compensate for command line length limits with a logical name

Sometimes, you might end up with a rather long compile line due to
excessively long /INCLUDE directories.  Compensate for it by making
a temporary logical name with them and using said logical name as
/INCLUDE argument.

A note was added to NOTES.VMS regarding these limitations.

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