pkg.in: bail out if anything goes wrong

Failing to kaboom just in time can make (and has just made)
it harder to figure out the culprit down the road; e.g.
metadata target's tar(1) might fail to find *some* files
that haven't been copied over due to a single one missing
by that run.

pkg.in/Makefile

@@ -8,5 +8,5 @@ endif
 # sequential execution, no reason to haste
 all:
 	@for dir in lists groups profiles; do \
-		$(MAKE) -C $$dir; \
+		$(MAKE) -C $$dir || exit; \
 	done