x86 soft-float feature: mark it as forbidden rather than unstable I am not sure why I made it "unstable" in https://github.com/rust-lang/rust/commit/f755f4cd1a2450da62b53f98f662d445f1f048b2; I think at the time "forbidden" did not work for some reason. Making it "forbidden" instead has no significant effect on `-Ctarget-feature` use, it just changes the warning. It *does* have the effect that one cannot query this using `cfg(target_feature)` on nightly any more, but that seems fine to me. It only ever worked as an accidental side-effect of f755f4cd1a2450da62b53f98f662d445f1f048b2 anyway. r? @workingjubilee