user build support for art (2 of 3)

Change-Id: I4696fee58e43db48540e2442c4235fc4bb02d9e3
diff --git a/build/Android.common.mk b/build/Android.common.mk
index c7bfbe5..853c4d2 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -31,6 +31,11 @@
 ART_CACHE_OUT := $(TARGET_OUT_DATA)/art-cache
 
 # $(1): pathname
+define art-cache-dir
+$(ART_CACHE_DIR)/$(subst /,@,$(1))
+endef
+
+# $(1): pathname
 define art-cache-out
 $(ART_CACHE_OUT)/$(subst /,@,$(1))
 endef