Add ART runtime to userdebug and eng builds to allow dual booting via developer options

Change-Id: Id3f2ffe92ca083853bd28f155a314612e8b1b2f6
diff --git a/target/product/core_minimal.mk b/target/product/core_minimal.mk
index cf499cb..313aee2 100644
--- a/target/product/core_minimal.mk
+++ b/target/product/core_minimal.mk
@@ -58,5 +58,8 @@
     uiautomator
 
 PRODUCT_RUNTIMES := runtime_libdvm_default
+ifneq (,$(filter userdebug eng, $(TARGET_BUILD_VARIANT)))
+    PRODUCT_RUNTIMES += runtime_libart
+endif
 
 $(call inherit-product, $(SRC_TARGET_DIR)/product/base.mk)