manually load fallback libc always load when no specific one exists

[psifertex]

I'd like to revisit the fact that the fallback type library right now has a specific list of hard-coded architectures and is not loaded for any others. At a minimum we should give users the ability to request it be loaded using open-with-options but we might even want to go as far as just enabling it by default and letting the user chose not to in the case where the fallback is less specific than another better set of headers they wish to import.