Generate Mac build artifact (#1406)

.github/workflows/cmake.yml

@@ -0,0 +1,48 @@
+name: CMake
+
+# When creating a new workflow in GitHub’s action builder the default trigger is the push event. We want to extend this to push and pull request events.
+on: [push, pull_request]
+
+env:
+  # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
+  BUILD_TYPE: Release
+
+jobs:
+  build:
+    # The CMake configure and build commands are platform agnostic and should work equally
+    # well on Windows or Mac.  You can convert this to a matrix build if you need
+    # cross-platform coverage.
+    # See: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
+    runs-on: macos-latest
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    
+    - name: Create Build Environment
+      run: brew bundle install
+
+    - name: Configure CMake
+      # Use a bash shell so we can use the same syntax for environment variable
+      # access regardless of the host operating system
+      shell: bash
+      working-directory: ${{github.workspace}}/build
+      # Note the current convention is to use the -S and -B options here to specify source 
+      # and build directories, but this is only available with CMake 3.13 and higher.  
+      # The CMake binaries on the Github Actions machines are (as of this writing) 3.12
+      run: cmake ..
+
+    - name: Build
+      working-directory: ${{github.workspace}}/build
+      shell: bash
+      # Execute the build.  You can specify a specific target with "--target <NAME>"
+      run: cmake --build . -j 2 --target package
+    
+    - name: Release
+      uses: softprops/action-gh-release@v1
+      if: startsWith(github.ref, 'refs/tags/')
+      with:
+        files: ${{github.workspace}}/build/devilutionx.dmg
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}