On mips64le, syscall.Getdents() and struct syscall.Dirent do
not fit together, causing our parseDirents() implementation to
return garbage ( see https://github.com/rfjakob/gocryptfs/issues/200
and https://github.com/golang/go/issues/23624 ).

Switch to unix.Getdents which does not have this problem -
the next Go release with the syscall package fixes is too
far away, and will take time to trickle into distros.

This issue has been reported by Debian maintainer
Felix Lechner.