Xcode 12.4 actually works with -fopenmp, you need to add -Xclang option just before it.

I made a small sample code like this:

int main(int argc, const char * argv[]) {
omp_set_num_threads(8);
#pragma omp parallel
#pragma omp critical
NSLog(@"Greetings from thread %d", omp_get_thread_num());
return NSApplicationMain(argc, argv);
}

And I get this on the console:

2021-10-20 16:23:46.653740-0700 Test[14661:304853] Greetings from thread 0
2021-10-20 16:23:46.653954-0700 Test[14661:304941] Greetings from thread 1
2021-10-20 16:23:46.653985-0700 Test[14661:304943] Greetings from thread 3
2021-10-20 16:23:46.654015-0700 Test[14661:304942] Greetings from thread 2
2021-10-20 16:23:46.654045-0700 Test[14661:304944] Greetings from thread 4
2021-10-20 16:23:46.654069-0700 Test[14661:304947] Greetings from thread 7
2021-10-20 16:23:46.654085-0700 Test[14661:304946] Greetings from thread 6
2021-10-20 16:23:46.654102-0700 Test[14661:304945] Greetings from thread 5

My problem now is with libraw:

In the Makefile.dist, I uncommented CFLAGS+=-fopenmp and I added -Xclang to it, so it looks like:

CFLAGS+=-Xclang -fopenmp

It compiles fine, but when I linked my project, it'll link even I did not have libomp.dylib. So libraw is not really compiled with OpenMP support with the CFLAGS line above.

So what else is missing?