setup function could eliminate checks for features that are a subset of others

[parched]

If the macro had knowledge of what features were super sets of others, it could avoid extra feature checks. Currently it is up to the user to eliminate these by hand.

[pedrocr]

An even better solution would be if branches that create the same instructions just get un-duplicated because features may not be duplicates but the extra instructions not actually be used. But maybe that's too low level and would require compiler changes. I do wonder if one of the optimizing passes already does that kind of cleanup. Maybe not.