libbinder_ndk: __ANDROID_NDK__ canary

Noticed recently that libbinder_ndk had a static variant. Adding this
canary so that there is an error if it is accidentally compiled into an
app. This is aimed as a protection against potential future variants.

Bug: 136027762
Test: N/A
Change-Id: I7eaf1c0f12d9891fbb2a2f1dbaae06f06d6545cf