make libnativewindow part of the NDK

Test: compiled
Bug: treble
Change-Id: I289ec1155a4dc5fe56ff3fd00eda54e851023569
diff --git a/libs/nativewindow/Android.bp b/libs/nativewindow/Android.bp
index d0e4161..9c5f096 100644
--- a/libs/nativewindow/Android.bp
+++ b/libs/nativewindow/Android.bp
@@ -20,6 +20,14 @@
     license: "NOTICE",
 }
 
+ndk_library {
+    name: "libnativewindow.ndk",
+    symbol_file: "libnativewindow.map.txt",
+
+    // Android O
+    first_version: "26",
+}
+
 cc_library {
     name: "libnativewindow",
     export_include_dirs: ["include"],