And there was a prior GSoC that began work on porting Minix to the Raspberri Pi that can be built upon:
Also regarding your steps, I know there was some kind of user thread solution already working in Minix but I don't know if it was libpthread. One of them should work at least. The goal should be to integrate these llvm tools into the minix repo itself and not pkgsrc.Please let me know if you're still interested in working on this project. I hope that you're well, safe and healthy!
Cheers,
-stux