Make RRO packages for system_ext

Until now, packages from system_ext don't create RRO packages, instead
it uses static overlay, but to make system_ext common, it should use
RRO.

Bug: 150820813
Test: m && check if there are RRO packages that use from system_ext apps
Change-Id: Id0ddb66adca07a6bb4dda66fbee49fd476ac5342
diff --git a/core/product.mk b/core/product.mk
index 25a9c44..364f0d8 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -193,6 +193,9 @@
 # Package list to apply enforcing RRO.
 _product_list_vars += PRODUCT_ENFORCE_RRO_TARGETS
 
+# Packages to skip auto-generating RROs for when PRODUCT_ENFORCE_RRO_TARGETS is set to *.
+_product_list_vars += PRODUCT_ENFORCE_RRO_EXEMPTED_TARGETS
+
 _product_list_vars += PRODUCT_SDK_ATREE_FILES
 _product_list_vars += PRODUCT_SDK_ADDON_NAME
 _product_list_vars += PRODUCT_SDK_ADDON_COPY_FILES