Reformat code according to 'gotip' rules.

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

pkg/fileutil/dir_unix.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows
 // +build !windows
 
 package fileutil

pkg/fileutil/dir_windows.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows
 // +build windows
 
 package fileutil

pkg/fileutil/lock_flock.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows && !plan9 && !solaris
 // +build !windows,!plan9,!solaris
 
 package fileutil

pkg/fileutil/lock_linux.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package fileutil

pkg/fileutil/lock_linux_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package fileutil

pkg/fileutil/lock_solaris.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build solaris
 // +build solaris
 
 package fileutil

pkg/fileutil/lock_unix.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows && !plan9 && !solaris && !linux
 // +build !windows,!plan9,!solaris,!linux
 
 package fileutil

pkg/fileutil/lock_windows.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows
 // +build windows
 
 package fileutil

pkg/fileutil/preallocate_darwin.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build darwin
 // +build darwin
 
 package fileutil

pkg/fileutil/preallocate_unix.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package fileutil

pkg/fileutil/preallocate_unsupported.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !linux && !darwin
 // +build !linux,!darwin
 
 package fileutil

pkg/fileutil/sync.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !linux && !darwin
 // +build !linux,!darwin
 
 package fileutil

pkg/fileutil/sync_darwin.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build darwin
 // +build darwin
 
 package fileutil

pkg/fileutil/sync_linux.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package fileutil

pkg/logutil/zap_journal.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows
 // +build !windows
 
 package logutil

pkg/logutil/zap_journal_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows
 // +build !windows
 
 package logutil

pkg/netutil/routes.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !linux
 // +build !linux
 
 package netutil

pkg/netutil/routes_linux.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package netutil

pkg/netutil/routes_linux_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package netutil

pkg/osutil/interrupt_unix.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows && !plan9
 // +build !windows,!plan9
 
 package osutil

pkg/osutil/interrupt_windows.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows
 // +build windows
 
 package osutil

pkg/osutil/signal.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !linux || cov
 // +build !linux cov
 
 package osutil

pkg/osutil/signal_linux.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux && !cov
 // +build linux,!cov
 
 package osutil

pkg/runtime/fds_other.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !linux
 // +build !linux
 
 package runtime

scripts/fix.sh

@@ -5,9 +5,15 @@ set -e
 source ./scripts/test_lib.sh
 source ./scripts/updatebom.sh
 
+# To fix according to newer version of go:
+# go get golang.org/dl/gotip
+# gotip download
+# GO_CMD="gotip"
+GO_CMD="go"
+
 function mod_tidy_fix {
   run rm ./go.sum
-  run go mod tidy || return 2
+  run ${GO_CMD} mod tidy || return 2
 }
 
 function bash_ws_fix {
@@ -23,7 +29,7 @@ function bash_ws_fix {
 log_callout -e "\\nFixing etcd code for you...\\n"
 
 run_for_modules mod_tidy_fix || exit 2
-run_for_modules run go fmt || exit 2
+run_for_modules run ${GO_CMD} fmt || exit 2
 run_for_module tests bom_fix || exit 2
 bash_ws_fix || exit 2
 

server/embed/config_logging_journal_unix.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows
 // +build !windows
 
 package embed

server/embed/config_logging_journal_windows.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows
 // +build windows
 
 package embed

server/mvcc/backend/config_default.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !linux && !windows
 // +build !linux,!windows
 
 package backend

server/mvcc/backend/config_windows.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows
 // +build windows
 
 package backend

tests/e2e/cluster_direct_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 package e2e

tests/e2e/cluster_proxy_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build cluster_proxy
 // +build cluster_proxy
 
 package e2e

tests/e2e/ctl_v3_auth_no_proxy_test.go

@@ -14,6 +14,7 @@
 
 // These tests depends on certificate-based authentication that is NOT supported
 // by gRPC proxy.
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 package e2e

tests/e2e/ctl_v3_watch_cov_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build cov
 // +build cov
 
 package e2e

tests/e2e/ctl_v3_watch_no_cov_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cov
 // +build !cov
 
 package e2e

tests/e2e/etcd_spawn_cov.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build cov
 // +build cov
 
 package e2e

tests/e2e/etcd_spawn_nocov.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cov
 // +build !cov
 
 package e2e

tests/e2e/v2_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !v2v3
 // +build !v2v3
 
 package e2e

tests/e2e/v2v3_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build v2v3
 // +build v2v3
 
 package e2e

tests/e2e/v3_cipher_suite_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cov && !cluster_proxy
 // +build !cov,!cluster_proxy
 
 package e2e

tests/integration/clientv3/connectivity/black_hole_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 package connectivity_test

tests/integration/clientv3/connectivity/network_partition_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 package connectivity_test

tests/integration/clientv3/watch_fragment_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 package clientv3test

tests/integration/cluster_direct.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 package integration

tests/integration/cluster_proxy.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build cluster_proxy
 // +build cluster_proxy
 
 package integration

tests/integration/embed/embed_proxy_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build cluster_proxy
 // +build cluster_proxy
 
 // The purpose of this (empty) package is too keep following test working:

tests/integration/embed/embed_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !cluster_proxy
 // +build !cluster_proxy
 
 // Keep the test in a separate package from other tests such that

tests/integration/v2store/store_tag_not_v2v3_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !v2v3
 // +build !v2v3
 
 package v2store_test

tests/integration/v2store/store_tag_v2v3_test.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build v2v3
 // +build v2v3
 
 package v2store_test

tools/etcd-dump-metrics/install_darwin.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build darwin
 // +build darwin
 
 package main

tools/etcd-dump-metrics/install_linux.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build linux
 // +build linux
 
 package main

tools/etcd-dump-metrics/install_windows.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows
 // +build windows
 
 package main