Attempt to fix Ubuntu builds

Author: MaxDesiatov

.github/workflows/main.yml

@@ -19,7 +19,7 @@ jobs:
       - name: Free disk space
         run: |
           df -h
-          sudo apt-get purge libgcc-9-dev gcc-9 libstdc++-9-dev
+          sudo apt-get purge libgcc-9-dev gcc-9 libstdc++-9-dev clang-6.0 llvm-6.0
           sudo swapoff -a
           sudo rm -f /swapfile
           sudo rm -rf /opt/hostedtoolcache