In practices adds annotations in the new syntax: ``` +//go:build !linux // +build !linux ``` Fixes failing gotip PASSES='fmt' check: https://travis-ci.com/github/etcd-io/etcd/jobs/486453806
A call file.Sync on OSX doesn't guarantee actual persistence on physical drive media as the data can be cached in physical drive's buffers. Hence calls to file.Sync need to be replaced with fcntl(F_FULLFSYNC).
