どの feature も単体での指定だと問題なかったですね．--enable-gc --enable-reference-types の組み合わせも試しましたが問題なかったので，どれか一つの feature が原因じゃなくて複合的に指定した時だけの問題っぽいです．流石に組合せ数が...

$ wasm-opt --help | grep enable- | awk -F' ' '{print $1}' | xargs -I{} fish -c "echo {} && wasm-opt -Oz {} hoge.wasm -o hoge_host_opt.wasm && wasmtime hoge_host_opt.wasm" --enable-sign-ext warning: active memory segments have overlap, which prevents some optimizations. Hello, world! --enable-threads warning: active memory segments have overlap, which prevents some optimizations. Hello, world! --enable-mutable-globals warning: active memory segments have overlap, which prevents some optimizations. Hello, world! 以下略