Don't build everything for APKCERTS_FILE

Before this change, to build APKCERTS_FILE you have to build any modules
in the system first, which include modules that only need to be checked,
instead of being built. This can reduce the build time when "dist" is

Change-Id: I64bee67977adcaf7b7c8df3f8f6492c9c33bc69d
diff --git a/core/Makefile b/core/Makefile
index 3d92b60..35773bf 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -215,16 +215,9 @@
 intermediates := \
 	$(call intermediates-dir-for,PACKAGING,apkcerts)
 APKCERTS_FILE := $(intermediates)/$(name).txt
-# Depending on the built packages isn't exactly right,
-# but it should guarantee that the apkcerts file is rebuilt
-# if any packages change which certs they're signed with.
-all_built_packages := $(foreach p,$(PACKAGES),$(ALL_MODULES.$(p).BUILT))
-ifneq ($(TARGET_BUILD_APPS),)
-# We don't need to really build all the modules for apps_only build.
+# We don't need to really build all the modules.
+# TODO: rebuild APKCERTS_FILE if any app change its cert.
-$(APKCERTS_FILE): $(all_built_packages)
 	@echo APK certs list: $@
 	@mkdir -p $(dir $@)
 	@rm -f $@
@@ -238,7 +231,9 @@
 .PHONY: apkcerts-list
 apkcerts-list: $(APKCERTS_FILE)
-$(call dist-for-goals, apps_only, $(APKCERTS_FILE):apkcerts.txt)
+ifneq (,$(TARGET_BUILD_APPS))
+  $(call dist-for-goals, apps_only, $(APKCERTS_FILE):apkcerts.txt)
 # -----------------------------------------------------------------
 # module info file