Fix Android.mk to use LOCAL_MODULE_TAGS.

Change-Id: Id7e36793e300077cdfc9a3849c574570af8fb76b
diff --git a/Android.mk b/Android.mk
index ddbc353..1d2f735 100644
--- a/Android.mk
+++ b/Android.mk
@@ -20,6 +20,8 @@
 
 include $(CLEAR_VARS)
 
+LOCAL_MODULE_TAGS := optional
+
 LOCAL_CPP_EXTENSION := .cc
 
 LOCAL_SRC_FILES:= $(libgabi++_common_src_files)
@@ -36,6 +38,8 @@
 
 include $(CLEAR_VARS)
 
+LOCAL_MODULE_TAGS := optional
+
 LOCAL_CPP_EXTENSION := .cc
 
 LOCAL_SRC_FILES:= $(libgabi++_common_src_files)