Add MinGW to CI

.github/workflows/windows.yml

@@ -67,3 +67,26 @@ jobs:
       run: ctest -C ${{matrix.build_type}} -V
       env:
         CTEST_OUTPUT_ON_FAILURE: True
+
+  mingw:
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    strategy:
+      matrix:
+        sys: [ mingw64, mingw32, ucrt64 ]
+    steps:
+    - uses: msys2/setup-msys2@v2
+      with:
+        release: false
+        msystem: ${{matrix.sys}}
+        pacboy: cc:p cmake:p ninja:p lld:p
+    - uses: actions/checkout@v2
+    - name: Configure
+      run: cmake -B ../build -DBUILD_SHARED_LIBS=ON -DCMAKE_BUILD_TYPE=Debug
+      env: { LDFLAGS: -fuse-ld=lld }
+    - name: Build
+      run: cmake --build ../build
+    - name: Test
+      run: ctest -j `nproc` --test-dir ../build