[Dlang-internal] (De)Duplication of information in DRuntime

[Brian]

Hello all --

I posted a DRuntime PR 
(https://github.com/dlang/druntime/pull/3577) syncing OpenBSD 
dlfcn.h defines.

I noticed that some of this dlfcn information is both in the 
OS-specific dlfcn.d file and the POSIX dlfcn.d file. Worse still, 
the OpenBSD-specific version of dlfcn.d is markedly different 
than the FreeBSD and NetBSD specific versions of dlfcn.d. The 
FreeBSD and NetBSD specific versions of dlfcn.d duplicate 
information that appears in the POSIX dlfcn.d file (e.g., the 
Dl_info struct) whereas the OpenBSD version does not have (as 
much) duplication of effort.

That leads to a few questions...
1. Is there some sort of standard rule for which duplicated 
effort wins?
2. Is deduplication desirable?
3. (and most immediately important) Should I be keeping my PR 
as-is or should I make the OpenBSD dlfcn.d look more like the 
FreeBSD and NetBSD versions?

Thanks.

~Brian