I'm sorry I wasn't clear. I'll try again.
First, some needed background.
- The port produces the binary package. There is no functional difference between building from the port, and installing the binary package from a nearby mirror.
- The port's Makefile explicitly disables libgomp, the library for Gnu Offload and Multi Processing, using the OpenMP standard.
Now, I'll try to be clearer:
- You cannot build Gnu OpenMP applications on OpenBSD today. No one has stepped up to port OpenMP to OpenBSD.
- The header file you want to use requires the disabled OpenMP library. It's only purpose is to provide OpenMP programming interfaces.
Unless and until OpenMP is ported, if you require an OpenMP application, you will need to use a different OS.