Enable art for user builds

Bug: 10069754
Change-Id: Iaaff33a97bd7b68b2e8d84cd0034b15dde8a4316
diff --git a/core/package.mk b/core/package.mk
index fd72cce..551028c 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -153,7 +153,7 @@
 ifeq (,$(LOCAL_APK_LIBRARIES))
 ifneq (,$(LOCAL_SRC_FILES))
 ifndef LOCAL_DEX_PREOPT
-LOCAL_DEX_PREOPT := true
+LOCAL_DEX_PREOPT := $(DEX_PREOPT_DEFAULT)
 endif
 endif
 endif