Small fixes required:
* `ExitStatusExt` differs because UNIX expects exit code to be `i32`
whereas Windows does `u32`
* Marking a file "executable only by owner" is a bit more involved on
Windows. We just do something approximate for now (and add a TODO) to
get things compiling.
I created this PR on my personal Windows machine and `cargo test` and
`cargo clippy` succeed. Once this is in, I'll rebase
https://github.com/openai/codex/pull/665 on top so Windows stays fixed!
c18f1689a9