libarchive: fix harness and improve build setup

[Mrmaxmeier]

This fixes a major harness issue in the libarchive fuzzer and resolves a fuzzing roadblock issue related to the build setup. All calls after archive_read_add_passphrase currently exit early because the decoder state is marked as invalid due to incorrect API usage.

When combined with https://github.com/libarchive/libarchive/pull/2229, this should improve coverage from ~15% to >45%. While the harness issue regressed at some point, it seems like the CRC build flag issue was always present in oss-fuzz's libarchive setup.

Thanks!