syscall.Dup2 is not available on arm64, this breaks building containerd on arm64 after containerd/containerd#4657

It looks like golang/sys@9d4e42a has a wrapper in golang.org/x/sys/unix.Dup2

https://golang.org/pkg/syscall/ says:

Deprecated: this package is locked down. Callers should use the corresponding package in the golang.org/x/sys repository instead. That is also where updates required by new systems or versions should be applied. See https://golang.org/s/go1.4-syscall for more information.

So I think we should probably just switch the package out.