I see this as quite unfortunate, sadly. These are all just initializer patterns, none of them are meant to be used. Requiring them to be `mut` means that you could in theory write `INIT_ATOMIC_UINT.fetch_add(1)` which seems... bad.

@brson, I suppose for now these should be `static mut`. cc @nikomatsakis, this is an unforseen case in statics that I didn't think of earlier sadly.