CI: Add MacOS build (#178)

.github/workflows/qmake.yml

@@ -83,3 +83,39 @@ jobs:
         Invoke-WebRequest -Uri "https://download.qt.io/official_releases/jom/jom.zip" -OutFile jom.zip
         unzip jom.zip
         .\jom
+
+  build-mac:
+    name: MacOS build
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Cache Qt
+      id: cache-qt
+      uses: actions/cache@v1  # not v2!
+      with:
+        path: ../Qt
+        key: ${{ runner.os }}-QtCache
+
+    - name: Install Qt
+      uses: jurplel/install-qt-action@v2
+      with:
+        version: '5.15.2'
+        host: 'mac'
+        target: 'desktop'
+        install-deps: 'true'
+        modules: 'qtwebengine'
+        cached: ${{ steps.cache-qt.outputs.cache-hit }}
+        setup-python: 'true'
+        tools: ''
+        set-env: 'true'
+        tools-only: 'false'
+
+    - name: MacOS and Qt version
+      run: |
+        sw_vers
+        echo number of processors: $(sysctl -n hw.ncpu)
+        qmake -v
+    - name: qmake
+      run: qmake qskinny.pro
+    - name: make
+      run: make -j$(sysctl -n hw.ncpu)