Add make rule for dex.

(cherry-picked from commit 6f567f2bcbd07375c723e03c994a7c7674f42c7e)

Change-Id: If3c7122d7a6e914d4a21a33d0dddcc234bb5089e
diff --git a/JavaLibrary.mk b/JavaLibrary.mk
index a28e609..673c0bf 100644
--- a/JavaLibrary.mk
+++ b/JavaLibrary.mk
@@ -149,6 +149,12 @@
 # Build for the host.
 #
 
+include $(CLEAR_VARS)
+LOCAL_SRC_FILES := $(call all-main-java-files-under, dex)
+LOCAL_MODULE_TAGS := optional
+LOCAL_MODULE := dex-host
+include $(BUILD_HOST_JAVA_LIBRARY)
+
 ifeq ($(WITH_HOST_DALVIK),true)
 
     # Definitions to make the core library.