x86: support mapdir on wasi

[ktock]

This commit adds support for --mapdir for x86_64(bochs)-based containers.
This is done by porting TinyEMU's virtio-9p implementation to bochs.
Now wasi runtimes shares files to bochs via WASI(--mapdir) and bochs shares these files to the guest Linux VM via virtio-9p.

$ make
$ ./out/c2w --assets=. alpine:3.17 /tmp/out/out.wasm
$ mkdir -p /tmp/share/ && echo hi > /tmp/share/from-host
$ wasmtime --mapdir /mnt/share::/tmp/share /tmp/out/out.wasm cat /mnt/share/from-host
hi