install clang?

i really hate github actions lmao this sucks

.github/workflows/c-cpp.yml

@@ -29,6 +29,7 @@ jobs:
     - uses: actions/checkout@v2
     - name: build-clang
       run: |
+          sudo apt-get install -y clang-12 clang++-12
           mkdir build 
           cd build
           export CXX=clang++-12