@3405691582 ok, your suggestions did work for building llvm.
However when building swift I get the following error. I am on OpenBSD 7.0, swift is on main branch.
stdlib/public/stubsStubs.cpp:539:45: error: use of undeclared identifier 'pthread_attr_get_np'
Could it be that the main branch has changed since [docs] Update for OpenBSD 7.1. by 3405691582 · Pull Request #39893 · apple/swift · GitHub and that it does not build anymore?
Yes, there is a buildbreak at HEAD for OpenBSD (only). Please pick #39995 until this is merged upstream or checkout main at a different point.
I noticed that #39995 has been merged. I pulled and it built flawlessly.
Thanks 
One more thing: now that I managed to build for amd64, I would like to port it to arm64 on OpenBSD.
Would you be happy to give me some guidance with that? I'll do the hard work, I'll just need some of your experience
Feel free to do the work. I don't know if any special work will be required, though testing on different hardware is always a good idea.
You can always ask me or others questions on the forums here, though you should probably start a new thread for further questions, though, as we have gone entirely offtopic here.
ok thanks :-)