stage2-based debug fixup

Employed double colon targets to eliminate
  warning: ignoring old commands for target `debug'

features.in/install2/install2/stage2cfg.mk

@@ -11,7 +11,7 @@ HSH_EXCLUDE_DOCS = 1
 # pass downstream
 GLOBAL_BASE_BOOTLOADER := $(BASE_BOOTLOADER)
 
-debug:
+debug::
 	@echo "** install2: IMAGE_PACKAGES: $(IMAGE_PACKAGES)"
 	@echo "** install2: IMAGE_PACKAGES_REGEXP: $(IMAGE_PACKAGES_REGEXP)"
 	@echo "** install2: CLEANUP_PACKAGES: $(CLEANUP_PACKAGES)"

features.in/rescue/rescue/stage2cfg.mk

@@ -7,6 +7,6 @@ IMAGE_PACKAGES = $(COMMON_PACKAGES) \
 
 MKI_PACK_RESULTS = squash:rescue
 
-debug:
+debug::
 	@echo "** rescue: IMAGE_PACKAGES: $(IMAGE_PACKAGES)"
 	@echo "** rescue: IMAGE_PACKAGES_REGEXP: $(IMAGE_PACKAGES_REGEXP)"

sub.in/stage2/Makefile

@@ -43,4 +43,4 @@ all: | $(GLOBAL_DEBUG) build-image run-image-scripts pack-image \
 	$(GLOBAL_CLEAN_WORKDIR)
 
 # dummy
-debug: ;
+debug:: ;