layout: Show a warning if no region is included

This seems better than a plain success message for a (probably
accidental) no-op run.

Change-Id: I53b749ce42ecc6c267b6cbe71413d536ec3965c5
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/313
Reviewed-by: Felix Singer <felixsinger@posteo.net>
diff --git a/include/layout.h b/include/layout.h
index 356ca25..c64dc01 100644
--- a/include/layout.h
+++ b/include/layout.h
@@ -56,6 +56,7 @@
 
 int register_include_arg(struct layout_include_args **, char *arg);
 int process_include_args(struct flashprog_layout *, const struct layout_include_args *);
+unsigned int layout_num_regions_included(const struct flashprog_layout *);
 void cleanup_include_args(struct layout_include_args **);
 
 const struct romentry *layout_next_included_region(const struct flashprog_layout *, chipoff_t);