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
File lock interface was more verbose than it needed to be while simultaneously making it difficult to support systems (e.g., Windows) that only permit locked writes on a single fd holding the lock.
