Snippets for nix 2.32.4 from FreeBSD 151arm64

Sourced from https://pkg-status.freebsd.org/ampere5/data/latest-per-pkg/nix/2.32.4_6/151arm64-default.log.

• ../src/libutil/hash.cc:298:14: warning: unused variable 'blake3TbbThreshold' [-Wunused-const-variable]
    298 | const size_t blake3TbbThreshold = 128000;
        |              ^~~~~~~~~~~~~~~~~~