Add WITH_DEXPREOPT to the list of protected global variables.

Bug: 14380196
Change-Id: I02cff39eeaf2deddf434c0c310063e4b341edd43
diff --git a/core/product.mk b/core/product.mk
index cf6fb9a..fd405ad 100644
--- a/core/product.mk
+++ b/core/product.mk
@@ -252,7 +252,8 @@
 
 
 _product_stash_var_list += \
-	DEFAULT_SYSTEM_DEV_CERTIFICATE
+	DEFAULT_SYSTEM_DEV_CERTIFICATE \
+	WITH_DEXPREOPT
 
 #
 # Stash values of the variables in _product_stash_var_list.