Allow build on FreeBSD

Created by: iori-yja

These commits change two things:

• shebangs of shell scripts This change also helps other environments that place bash on where else of /bin (such like /usr/bin, /usr/local/bin or in-busybox, wherever). Yes, this change relies on env command being available and placed in /usr/bin, that is confirmed as so on Mac OS, Ubuntu, Arch Linux and FreeBSD.

• submodule information of libc-artifacts (to pointing out https://github.com/redox-os/libc-artifacts/pull/7) This change is as above one but for libc-artifacts submodule; this fix is already pull-requested to the repository, and this change is only for repointing it.

Created by: iori-yja

Hmm... the check is failed because the new commit that submodule refers is not merged in libc-artifacts repository. I don't think I could do with this except waiting the commit is merged.

Thanks!