Run the CI in clang

.github/workflows/build-and-test.yml

@@ -5,8 +5,13 @@ on: [pull_request, push]
 jobs:
   build:
     runs-on: ubuntu-latest
-
     steps:
       - uses: actions/checkout@v2
       - name: Build
         run: make test
+  build-ubuntu-clang:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Build
+        run: CC=clang CXX=clang++ make test