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>

NOTES.VMS

@@ -5,8 +5,8 @@
  Requirement details
  -------------------
 
- In addition to the requirements listed in INSTALL, these are required
- as well:
+ In addition to the requirements and instructions listed in INSTALL,
+ this are required as well:
 
   * At least ODS-5 disk organization for source and build.
     Installation can be done on any existing disk organization.
@@ -22,6 +22,17 @@
  a different ANSI C compiler may require some work.
 
 
+ About MMS and DCL
+ -----------------
+
+ MMS has certain limitations when it comes to line length, and DCL has
+ certain limitations when it comes to total command length.  We do
+ what we can to mitigate, but there is the possibility that it's not
+ enough.  Should you run into issues, a very simple solution is to set
+ yourself up a few logical names for the directory trees you're going
+ to use.
+
+
  Checking the distribution
  -------------------------