This seems to be more correct than what we previously had with fewer lines of code, so I like that. I still don't really like the extra flag I had to add for Nt{Create,Open}Key, but I couldn't find a way to make things work without it. I also checked that Windows doesn't use a similar flag (by iterating over all bit masks).
I don't think we want to add a Wine-specific flag. There has to be a way of doing that with the existing APIs.