Cirrus-CI: Run check-ldirs in include/

Check that LDIRS defined in include/Makefile actually exist.

Reviewed by:	emaste
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D39681

.cirrus.yml

@@ -60,6 +60,10 @@ task:
   - make sysent
   - if ! git diff --exit-code; then printf "\n>>> Generated sysent files not updated, run make sysent <<<\n"; false; fi
 
+  include_ldirs_script:
+  # Check that includes/Makefile refers to existing directories
+  - if ! make -C include/ check-ldirs; then printf "\n>>> include/Makefile lists nonexistant directories <<<\n"; false; fi
+
   post_script:
   - df -m
   - du -m -s /usr/obj