Makefile, lib/build.mk: fix usage AUTOCLEAN with DEBUG

make distclean should be launched after copying the log when
debugging is enabled.

Makefile

@@ -69,6 +69,7 @@ SHELL = /bin/bash
 		else \
 			exit 1; \
 		fi; \
+		if [ -n "$(AUTOCLEAN)" ]; then $(MAKE) distclean; fi; \
 	done; \
 	if [ "$$n" -lt "$(NUM_TARGETS)" ]; then say; fi
 

lib/build.mk

@@ -103,7 +103,6 @@ build-image: profile/populate
 		df -P $(BUILDDIR) | awk 'END { if ($$4 < $(LOWSPACE)) \
 			{ print "NB: low space on "$$6" ("$$5" used)"}}'; \
 	fi; \
-	if [ -n "$(AUTOCLEAN)" -a $$RETVAL = 0 ]; then $(MAKE) distclean; fi; \
 	if [ -n "$(BELL)" ]; then echo -ne '\a'; fi; \
 	exit $$RETVAL; \
 	} >&2