libbinder_ndk: use c++17

For std::optional for nullable types.

Bug: 111445392
Test: atest android.binder.cts
Change-Id: If212473b4b051197be42d782f25777a5795f11dd
diff --git a/libs/binder/ndk/Android.bp b/libs/binder/ndk/Android.bp
index d16502f..14ce4cb 100644
--- a/libs/binder/ndk/Android.bp
+++ b/libs/binder/ndk/Android.bp
@@ -39,6 +39,8 @@
         "libutils",
     ],
 
+    cpp_std: "c++17",
+
     version_script: "libbinder_ndk.map.txt",
 }