Add libnativehelper to root Android.bp

libnativehelper has an Android.bp file, so it won't cause a namespace
conflict between the glob on the directory and the module name.

Bug: 25797955
Change-Id: Id86b3a1cd0f130989f77613494e19b8f255029ce
diff --git a/root.bp b/root.bp
index b3d1674..0a8c0c3 100644
--- a/root.bp
+++ b/root.bp
@@ -15,6 +15,7 @@
     "frameworks/native/libs/*",
     "hardware/*",
     "libcore",
+    "libnativehelper",
     "packages/apps/HTMLViewer",
     "prebuilts/ndk",
     "prebuilts/sdk",