Accept external debug flag in native code

Change-Id: I762fd9025ffd6518daf42903875d6ca0a5389ff4
diff --git a/native/jni/Android.mk b/native/jni/Android.mk
index 237f19d..df98680 100644
--- a/native/jni/Android.mk
+++ b/native/jni/Android.mk
@@ -17,7 +17,7 @@
 ############ some local flags
 # If you change any of those flags, you need to rebuild both libjni_latinime_static
 # and the shared library.
-#FLAG_DBG := true
+FLAG_DBG ?= false
 FLAG_DO_PROFILE ?= false
 
 ######################################