In the default LLVM provided by Apple in macOS 10.13, High Sierra, is OpenMP finally available? It has been available in main LLVM for more than a year now.
(another
Standard Apple's clang supports OpenMP. They just disabled the driver option. But you can use the frontend option instead this way: clang -Xclang -fopenmp
Also, you need to set DYLD_LIBRARY_PATH environmental variable: export DYLD_LIBRARY_PATH=
How to get/build libomp.
$ cd
$ svn co http://llvm.org/svn/llvm-project/openmp/trunk libomp
$ cd libomp
$ mkdir build && cd build
$ cmake -DCMAKE_INSTALL_PREFIX=~/libomp/openmp
$ make && make install
After this directory ~/libomp/openmp will have 2 subdirs: include and lib, which should be used as the path to omp.h and the path to libomp.dylib correspondingly.
See also my answer to Is C++ compilable with OpenMP and boost on MacOS?