warning: unexpected `cfg` condition value: `unk`
  --> $DIR/order-independant.rs:13:7
   |
LL | #[cfg(a = "unk")]
   |       ^^^^^^^^^
   |
   = note: expected values for `a` are: (none), `b`
   = help: to expect this configuration use `--check-cfg=cfg(a, values("unk"))`
   = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
   = note: `#[warn(unexpected_cfgs)]` on by default

warning: 1 warning emitted