This package is imported to Android and uses Android's external/grpc-grpc
header files and compilation flags to generate bindings.

The Android.bp file is manually written due to:
    1. Binding to Android's existing copy of grpc instead of
       the copy that is bundled within the crate.
    2. The crates customized grpc_wrap.cc file that provides
       additional translation logic.
    3. A lot of bindgen customizations in build.rs.

The following line is added to android/bindgen_wrapper.h. It's unclear why this
is necessary, but building the grpcio crate fails without it.
#include <grpc/support/cpu.h>

If features are changed for the grpcio-sys crate, please ensure those
features are changed in the grpcio_bindgen module.