There are a boat load of tools for cross compiling between architectures on OpenBSD, but:
- They are NOT maintained, except when needed by the developer(s) porting the OS to a new architecture.
- They are NOT supported by the project for those outside the development team.
- The developers will NOT answer questions about the tools, for reasons #1 and #2 above.
- Anyone not a developer will not be able to help, due to #1, #2, and #3 above.
There have been presentations published at conferences that mention cross compiling efforts for new platforms. You should start your research with those. It is possible that if you posted a very polite query on misc@, a developer might give you some direction.