Modify update script to use top-of-tree for support library

Moves multidex out of support/ since it's not part of the build.

Test: ./update_current.py <build-id> --support
Bug: 62377528
Change-Id: I21f2d9df8ecd89792509abeec3422ca3000f9990
diff --git a/current/Android.mk b/current/Android.mk
index c3c5b79..d176031 100644
--- a/current/Android.mk
+++ b/current/Android.mk
@@ -23,9 +23,17 @@
 # make target artifacts with prebuilts.
 ifneq ($(TARGET_BUILD_APPS),)
 include $(CLEAR_VARS)
-LOCAL_PREBUILT_STATIC_JAVA_LIBRARIES := \
+
+# Set up prebuilts for the core Support Library artifacts.
+LOCAL_PREBUILT_STATIC_JAVA_LIBRARIES += \
   $(patsubst $(LOCAL_PATH)/%,%,\
     $(shell find $(LOCAL_PATH)/support -name "*.jar"))
+
+# Set up prebuilts for additional non-core library artifacts.
+LOCAL_PREBUILT_STATIC_JAVA_LIBRARIES += \
+  $(patsubst $(LOCAL_PATH)/%,%,\
+    $(shell find $(LOCAL_PATH)/multidex -name "*.jar"))
+
 include $(BUILD_MULTI_PREBUILT)
 
 # Generates the v4, v13, and appcompat libraries with static dependencies.