linux CI: Add clang

Clang is stricter, especially when it comes to constexpr usage.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

.github/workflows/linux.yaml

@@ -33,3 +33,32 @@ jobs:
 
       - name: Run tests
         run: ctest --test-dir _build
+  Linux-Clang:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        cxx: ['7', '17']
+    env:
+      CMAKE_OPTIONS: -DDEV_MODE=ON -DBUILD_TESTING=ON -DCMAKE_CXX_FLAGS="-stdlib=libc++"
+    steps:
+      - uses: lukka/get-cmake@latest
+      - uses: egor-tensin/setup-clang@v1
+        with:
+          version: ${{matrix.cxx}}
+        run: |
+          sudo apt install -y libc++abi-${{matrix.cxx}}-dev libc++-${{matrix.cxx}}-dev
+
+      - name: Get pushed code
+        uses: actions/checkout@v3
+
+      - name: Configure
+        run: cmake -S . -B _build ${{ env.CMAKE_OPTIONS }} -DCMAKE_INSTALL_PREFIX:STRING=${GITHUB_WORKSPACE}/_built
+
+      - name: Build
+        run: cmake --build _build --parallel
+
+      - name: Test installation
+        run: cmake --install _build --prefix ${GITHUB_WORKSPACE}/_built
+
+      - name: Run tests
+        run: ctest --test-dir _build