WireGuardKit: Add WireGuardKitCTarget with private C sources

Signed-off-by: Andrej Mihajlov <and@mullvad.net>

Package.swift

@@ -16,9 +16,14 @@ let package = Package(
     targets: [
         .target(
             name: "WireGuardKit",
-            dependencies: ["libwg-go"],
+            dependencies: ["libwg-go", "WireGuardKitCTarget"],
             path: "WireGuardKit/Sources/WireGuardKit"
         ),
+        .target(
+            name: "WireGuardKitCTarget",
+            dependencies: [],
+            path: "WireGuardKit/Sources/WireGuardKitCTarget"
+        ),
         .target(
             name: "libwg-go",
             dependencies: [],

WireGuardKit/Sources/WireGuardKit/PacketTunnelSettingsGenerator.swift

@@ -4,6 +4,7 @@
 import Foundation
 import Network
 import NetworkExtension
+import WireGuardKitCTarget
 
 class PacketTunnelSettingsGenerator {
     let tunnelConfiguration: TunnelConfiguration

WireGuardKit/Sources/WireGuardKitCTarget/include/WireGuardKitCTarget.h

@@ -0,0 +1,4 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+
+#include "../key.h"

WireGuardKit/Sources/WireGuardKitCTarget/module.modulemap

@@ -0,0 +1,4 @@
+module WireGuardKitCTarget {
+    umbrella header "include/WireGuardKitCTarget.h"
+    export *
+}