support vts compile mode flag

Change-Id: I05c347851cfc41c617b055209d81318a1a60918e
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 09032b2..1994e18 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -107,6 +107,7 @@
 LOCAL_MANIFEST_INSTRUMENTATION_FOR:=
 LOCAL_AIDL_INCLUDES:=
 LOCAL_VTS_INCLUDES:=
+LOCAL_VTS_MODE:=
 LOCAL_JARJAR_RULES:=
 LOCAL_ADDITIONAL_JAVA_DIR:=
 LOCAL_ALLOW_UNDEFINED_SYMBOLS:=