We now can handle these via `inc/maiko/platform.h` and the
constants defined there.
This doesn't change `OS5` for Solaris yet as that's a much wider
set of changes.
The NOFORN flag controls foreign function interface code, which
was written using the dld_* APIs which haven't existed in years.
There was a GNU dld that provided this API, but it was withdrawn
in 2006.
If this code is to be re-enabled, it will have to be changed to
use the `dlopen` family of APIs.
* Support building on OpenBSD, x86-64
* Clean up OpenBSD Makefile
* Add OpenBSD to cmake build
* Use clang as CC for OpenBSD
Co-authored-by: Alex Segura <alex@lispm.dev>