Change emma to be optional build target.
diff --git a/Android.mk b/Android.mk
index 7112f66..102f435 100644
--- a/Android.mk
+++ b/Android.mk
@@ -7,6 +7,8 @@
 
 LOCAL_MODULE := emma
 
+LOCAL_MODULE_TAGS := optional
+
 LOCAL_JAVA_RESOURCE_DIRS := core/res
 
 LOCAL_NO_EMMA_INSTRUMENT := true