Update

vendor/tailscale.com/syncs/mutex_debug.go

@@ -0,0 +1,22 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_mutex_debug
+
+package syncs
+
+import "sync"
+
+type Mutex struct {
+	sync.Mutex
+}
+
+type RWMutex struct {
+	sync.RWMutex
+}
+
+func RequiresMutex(mu *sync.Mutex) {
+	// TODO: check
+}
+
+// TODO(bradfitz): actually track stuff when in debug mode.