Switch from govendor to go modules. (#587)

Thanks to @BenoitKnecht for leading the way on this.

vendor/golang.org/x/sys/windows/race.go

@@ -0,0 +1,30 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build windows,race
+
+package windows
+
+import (
+	"runtime"
+	"unsafe"
+)
+
+const raceenabled = true
+
+func raceAcquire(addr unsafe.Pointer) {
+	runtime.RaceAcquire(addr)
+}
+
+func raceReleaseMerge(addr unsafe.Pointer) {
+	runtime.RaceReleaseMerge(addr)
+}
+
+func raceReadRange(addr unsafe.Pointer, len int) {
+	runtime.RaceReadRange(addr, len)
+}
+
+func raceWriteRange(addr unsafe.Pointer, len int) {
+	runtime.RaceWriteRange(addr, len)
+}