[rust_native_library] Use generic archiver for newer NDK versions

Summary: See here. Newer NDK versions don't ship with per-architecture archivers. People online suggest just using the generic llvm-ar, and it seemed to work in this case.

Test Plan: After applying a hack for the "Second issue" described in the above-linked Linear task, I was able to get past the rust_native_library step in the React Native Android build while using NDK versions 24.0.8215888

Reviewers: varun, jon, atul

Reviewed By: varun, atul

Subscribers: tomek, abosh

Differential Revision: https://phab.comm.dev/D5590