Move some debugging capabilities under #ifdef NN_DEBUGGABLE.

This makes them available under eng and userdebug but not user.

Bug: 63905942
Test: mm (userdebug and user)

Change-Id: I196c5df77290ed44a040e935adbf567f818e979d
diff --git a/Android.bp b/Android.bp
index 5a6c263..50849f5 100644
--- a/Android.bp
+++ b/Android.bp
@@ -27,6 +27,11 @@
         "-Wextra",
         "-Werror",
     ],
+    product_variables: {
+        debuggable: {  // eng and userdebug builds
+            cflags: ["-DNN_DEBUGGABLE"],
+        },
+    },
 }
 
 cc_library_headers {