Support to build host dex.

Change-Id: I55df5e4051dbeb89a70d6d7b89fb6110f133d9d7
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index c7343e5..c046c69 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -96,6 +96,7 @@
 LOCAL_PROGUARD_FLAGS:=
 LOCAL_EMMA_COVERAGE_FILTER:=
 LOCAL_MANIFEST_FILE:=
+LOCAL_BUILD_HOST_DEX:=
 
 # Trim MAKEFILE_LIST so that $(call my-dir) doesn't need to
 # iterate over thousands of entries every time.