1. Use Homebrew‘s LVM:

   brew install llvm

2. Then you have all the llvm binaries for /usr/local/opt/llvm/bin.

   Compile OpenMP Hello World. omp_hello.c

   /******************************************************************************
    * FILE: omp_hello.c
    * DESCRIPTION:
    * OpenMP Example - Hello World - C/C++ Version
    * In this simple example, the master thread forks a parallel region.
    * All threads in the team obtain their unique thread number and print it.
    * The master thread only prints the total number of threads. Two OpenMP
    * library routines are used to obtain the number of threads and each
    * thread's number.
    * AUTHOR: Blaise Barney 5/99
    * LAST REVISED: 04/06/05
    ******************************************************************************/
    #include <omp.h>
    #include <stdio.h>
    #include <stdlib.h>
   
    int main (int argc, char *argv[]) 
    {
    int nthreads, tid;
   
    /* Fork a team of threads giving them their own copies of variables */
    #pragma omp parallel private(nthreads, tid)
    {
   
    /* Obtain thread number */
    tid = omp_get_thread_num();
    printf("Hello World from thread = %d\n", tid);
   
    /* Only master thread does this */
    if (tid == 0) 
    {
    nthreads = omp_get_num_threads();
    printf("Number of threads = %d\n", nthreads);
    }
   
    } /* All threads join master thread and disband */
   
    }

   In a file and use

   /usr/local/opt/llvm/bin/clang -fopenmp -L/usr/local/opt/llvm/lib omp_hello.c -o hello

   It is possible that you will also need to replace CPPFLAGS by -I/usr/local/opt/llvm/include

   This is how the makefile should look

   CPP = /usr/local/opt/llvm/bin/clang
   CPPFLAGS = -I/usr/local/opt/llvm/include -fopenmp
   LDFLAGS = -L/usr/local/opt/llvm/lib
   
   omp_hello: omp_hello.c
    $(CPP) $(CPPFLAGS) $^ -o $@ $(LDFLAGS)

Up-to-date

You might encounter an error in macOS 10.14 (Mojave).

/usr/local/Cellar/llvm/7.0.1/lib/clang/7.0.1/include/omp.h:118:13: fatal error: 'stdlib.h' file not found

This could mean that the macOS SDK headers will be missing from /usr/include. They were moved to the SDK with Xcode 10. Install the headers to /usr/include

open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg