Always define apps_only

Allows dist-for-goals entries to use always use apps_only, without
having to conditionalize on TARGET_BUILD_APPS, or cause errors on full
platform builds.

Test: EMMA_INSTRUMENT=true m dist
Change-Id: Id484ad2a650b8ad49880469f195080ef7fa8c814
diff --git a/core/main.mk b/core/main.mk
index 1b00124..460cdf4 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1264,6 +1264,7 @@
 # dist_files only for putting your library into the dist directory with a full build.
 .PHONY: dist_files
 
+.PHONY: apps_only
 ifneq ($(TARGET_BUILD_APPS),)
   # If this build is just for apps, only build apps and not the full system by default.
 
@@ -1300,7 +1301,6 @@
   $(COVERAGE_ZIP) : $(apps_only_installed_files)
   $(call dist-for-goals,apps_only, $(COVERAGE_ZIP))
 
-.PHONY: apps_only
 apps_only: $(unbundled_build_modules)
 
 droid_targets: apps_only