Enhance/fix VMS exit code handling.

* commands.c, function.c, hash.c, job.c, main.c, output.c:
use MAKE exit codes.
* makeint.h: encode make exit codes so that they are VMS compatible.
* job.c: check child exit code for VMS style exit codes.
* vmsjobs.c: save and return VMS style exit code.

function.c

@@ -1610,7 +1610,7 @@ char *
 func_shell_base (char *o, char **argv, int trim_newlines)
 {
   fprintf (stderr, "This platform does not support shell\n");
-  die (EXIT_FAILURE);
+  die (MAKE_TROUBLE);
   return NULL;
 }