VMS: produce dependency files just like you produce object files

We need to do the same dance as when object files are created.
Reviewed-by: NViktor Dukhovni <viktor@openssl.org>

Configurations/descrip.mms.tmpl

@@ -445,7 +445,12 @@ configdata.pm : {- sourcefile("Configurations", "descrip.mms.tmpl") -} $(SRCDIR)
 
       return <<"EOF";
 $obj.MMS : $deps
+        ${before}
+        SET DEFAULT $forward
         \$(CC) \$(CFLAGS)${incs} /MMS=(FILE=${objd}${objn}.MMS,TARGET=$obj.OBJ) /NOOBJECT $srcs
+        SET DEFAULT $backward
+        ${after}
+        - PURGE $obj.MMS
 $obj.OBJ : $obj.MMS
         ${before}
         SET DEFAULT $forward