ART: Move libammtestjni to Android.bp

Avoids some weird build error under clang-tidy. The project cannot
be moved over completely, yet, as Soong is lacking JNI library
support for android_app.

Bug: 32619234
Test: WITH_TIDY=1 mmma art
Change-Id: I9f207501323a849619eb6fb9588e3a14eab8ce02