Add a comment in configdata.pm regarding script-only variables

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5247)

Configure

@@ -2304,6 +2304,8 @@ if ($builder eq "unified") {
 
 EOF
 }
+print OUT
+    "# The following data is only used when this files is use as a script\n";
 print OUT "my \%makevars = (\n";
 foreach (sort keys %user) {
     print OUT '    ',$_,' ' x (20 - length $_),'=> ',