setUpChildIo

fn setUpChildIo(
    sync: *CancelRegion.Sync,
    stdio: process.SpawnOptions.StdIo,
    pipe_fd: fd_t,
    std_fileno: i32,
    dev_null_fd: fd_t,
) !void {
    switch (stdio) {
        .pipe => try dup2(sync, pipe_fd, std_fileno),
        .close => _ = linux.close(std_fileno),
        .inherit => {},
        .ignore => try dup2(sync, dev_null_fd, std_fileno),
        .file => |file| try dup2(sync, file.handle, std_fileno),
    }
}