What changes were proposed in this pull request?

To make it easier for Apache Arrow to integrate with Apache ORC.

Why are the changes needed?

• Detect existing targets of 3rd-party dependencies from Apache Arrow, including: Protobuf, ZLIB, Snappy, and zstd.
• Note that lz4 does not need this change because Apache Arrow has already used FetchContent for it.

How was this patch tested?

Test it locally against Apache Arrow main branch.

-- Apache ORC: Using existing arrow::protobuf::libprotobuf
-- Apache ORC: Using existing Snappy::snappy-static
-- Apache ORC: Using existing ZLIB::ZLIB
-- Apache ORC: Using existing zstd::libzstd_static
-- Apache ORC: Using vendored lz4

Was this patch authored or co-authored using generative AI tooling?

No.