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: NRich Salz <rsalz@openssl.org>

Configurations/descrip.mms.tmpl

@@ -448,12 +448,19 @@ EOF
       my $srcs =
           join(", ",
                map { abs2rel(rel2abs($_), rel2abs($forward)) } @{$args{srcs}});
-      my $incs =
-          "/INCLUDE=(".join(",",
-                            map {
-                               file_name_is_absolute($_)
-                               ? $_ : catdir($backward,$_)
-                            } @{$args{incs}}).")";
+      my $incs_on = "\@ !";
+      my $incs_off = "\@ !";
+      my $incs = "";
+      if (@{$args{incs}}) {
+          $incs_on =
+              "DEFINE tmp_includes "
+              .join(",-\n\t\t\t", map {
+                                      file_name_is_absolute($_)
+                                      ? $_ : catdir($backward,$_)
+                                  } @{$args{incs}});
+          $incs_off = "DEASSIGN tmp_includes";
+          $incs = " /INCLUDE=(tmp_includes:)";
+      }
       my $before = $unified_info{before}->{$obj.".OBJ"} || "\@ !";
       my $after = $unified_info{after}->{$obj.".OBJ"} || "\@ !";
       my $depbuild = $disabled{makedepend} ? ""
@@ -463,7 +470,9 @@ EOF
 $obj.OBJ : $deps
         ${before}
         SET DEFAULT $forward
+        $incs_on
         \$(CC) \$(CFLAGS)${incs}${depbuild} /OBJECT=${objd}${objn}.OBJ /REPOSITORY=$backward $srcs
+        $incs_off
         SET DEFAULT $backward
         ${after}
         \@ PIPE ( \$(PERL) -e "use File::Compare qw/compare_text/; my \$x = compare_text(""$obj.MMS"",""$obj.tmp-MMS""); exit(0x10000000 + (\$x == 0));" || -

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
  -------------------------