Installation logs from a build of clang on Fedora without OpemMP support and R-devel configured with --disable-openmp . How to use OpenMP is described in detail in 'Writing R Extensions', and note the warnings in ยง1.6. Details as https://www.stats.ox.ac.uk/pub/bdr/Rconfig/r-devel-linux-x86_64-fedora-clang apart from the C/C++ compiler build, and the use of gfortran rather than flang-new.. Old results are done with old compiler versions.