Enforce no prebuilt apks in PRODUCT_COPY_FILES.

Bug: 5391935
Change-Id: I106ffc3277914e57cc1a6fb4cd782286d61b8013
diff --git a/core/Makefile b/core/Makefile
index a49850e..a3cfdd5 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -16,10 +16,16 @@
 # e.g., "system/etc/file.xml".
 # The filter part means "only eval the copy-one-file rule if this
 # src:dest pair is the first one to match the same dest"
+#$(1): the src:dest pair
+define check-product-copy-files
+$(if $(filter %.apk, $(1)),$(error \
+    Prebuilt apk found in PRODUCT_COPY_FILES: $(1), use BUILD_PREBUILT instead!))
+endef
 unique_product_copy_files_destinations :=
 $(foreach cf,$(PRODUCT_COPY_FILES), \
     $(eval _src := $(call word-colon,1,$(cf))) \
     $(eval _dest := $(call word-colon,2,$(cf))) \
+    $(call check-product-copy-files,$(cf)) \
     $(if $(filter $(unique_product_copy_files_destinations),$(_dest)),, \
         $(eval _fulldest := $(call append-path,$(PRODUCT_OUT),$(_dest))) \
         $(eval $(call copy-one-file,$(_src),$(_fulldest))) \