title: Enable OpenMP support in clang in Mac OS X (sierra & Mojave)
body: <p>I am using Mac OS X Sierra, and I found that clang (LLVM version 8.1.0 (clang-802.0.38)) does not support OpenMP:
  when I run <code>clang -fopenmp program_name.c</code>, I got the following error:</p>
  
  <p><code>clang: error: unsupported option '-fopenmp'</code></p>
  
  <p>It seems that clang does not support <code>-fopenmp</code> flag.</p>
  
  <p>I could not find any openmp library in homebrew. According to LLVM website, LLVM already supports OpenMP. But I could not find a way to enable it during compiling.</p>
  
  <p>Does this mean that the default clang in Mac does not support OpenMP?
   Could you provide any suggestions?</p>
  
  <p>(When I switch to GCC to compile the same program (gcc is installed using <code>brew install gcc --without-multilib</code>), and the compilation is successful.)</p>