GHA has now moved to 22.04. Installing "vanilla" clang via apt (which is clang-14) does not includeOpenMP include files and library. https://discourse.llvm.org/t/omp-h-not-found-after-fresh-install-with-apt-llvm-org-llvm-sh-wsl2-ubuntu-20-04/4549. Remedy is

sudo apt install libomp-dev