OpenMP not found

For work I need to install OpenMP (the CXX libraries to be specific). I installed the package llvmPackages.openmp but when I run my cmake I get the error Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES). What package do I need to install/ what am I doing wrong and how can I resolve this issue?