Package: android-platform-external-libunwind According to the source trees at both https://github.com/Unity-Technologies/android-libunwind and https://android.googlesource.com/platform/external/libunwind/, ppc64[le] systems are supported. However, the version in Debian, even Sid, explicitly removes and disables support for ppc66el.
Please update to the current version and re-enable ppc64el builds. There are several Android host-side tools, including adb, that are blocked partly by the lack of a build for this library on ppc64el.