This cmake project documents a cmake bug regarding OpenMP and IBM XL Fortran/C++.
Compiling this project with CC=xlc_r CXX=xlC_r FC=xlf_r cmake .. results in linking to -lxlomp_ser, which disables OpenMP in XL.
A workaround is to run cmake with explicit FFLAGS: CC=xlc_r CXX=xlC_r FC=xlf_r FFLAGS="-qsmp=omp" cmake ..
Bug report: https://gitlab.kitware.com/cmake/cmake/issues/18518