ipc, rwcancel: compile on js/wasm

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipc/uapi_js.go

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package ipc
+
+// Made up sentinel error codes for the js/wasm platform.
+const (
+	IpcErrorIO        = 1
+	IpcErrorInvalid   = 2
+	IpcErrorPortInUse = 3
+	IpcErrorUnknown   = 4
+	IpcErrorProtocol  = 5
+)

rwcancel/rwcancel.go

@@ -1,4 +1,4 @@
-//go:build !windows
+//go:build !windows && !js
 
 /* SPDX-License-Identifier: MIT
  *

rwcancel/rwcancel_stub.go

@@ -1,3 +1,5 @@
+//go:build windows || js
+
 // SPDX-License-Identifier: MIT
 
 package rwcancel