Mark more targets as PHONY

So that we can start restricting non-phony targets to $OUT_DIR and
$DIST_DIR.

Test: add --writable=out/, see fewer warnings
Change-Id: I411fe4af732b1bce35d4a4c1e2a47b5f8a15e6b8
diff --git a/core/base_rules.mk b/core/base_rules.mk
index b4cb55b..744740f 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -356,6 +356,7 @@
 ## make clean- targets
 ###########################################################
 cleantarget := clean-$(my_register_name)
+.PHONY: $(cleantarget)
 $(cleantarget) : PRIVATE_MODULE := $(my_register_name)
 $(cleantarget) : PRIVATE_CLEAN_FILES := \
     $(LOCAL_BUILT_MODULE) \