CI: enable macos builds

.github/workflows/macos.yml

@@ -0,0 +1,28 @@
+on: [push, pull_request, workflow_dispatch]
+
+permissions:
+  contents: read
+
+jobs:
+  build_and_test:
+    strategy:
+      matrix:
+        os: [macos-13, macos-12, macos-11]
+    name: ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install dependencies
+      run: |
+        brew install libsodium
+    - name: Compile 
+      run: |
+        ./configure
+        make -C build
+    - name: Test 
+      run: |
+        otool -L build/vpnserver
+        .ci/memory-leak-test.sh
+