package libunwind and libblocksruntime with honggfuzz

Currently, using honggfuzz + rules_fuzzing requires users to install libunwind-dev and libblocksruntime-dev. Users might also need to configure their bazel toolchains to support these dependencies.

I would prefer to see these dependencies packaged with rules_fuzzing, so that honggfuzz would build more hermetically. Preferably we could bazelify and build these dependencies from source; alternatively we can supply binaries.

Start by reviewing how rules_fuzzing currently wires honggfuzz and where users configure Bazel toolchains for libunwind-dev and libblocksruntime-dev. Done means honggfuzz builds hermetically with these dependencies packaged from source or supplied as binaries, without requiring users to install them separately.

Written by the indexing model from the issue text.