06f0adb345
move core::hint::black_box under its own feature gate The `black_box` function had its own RFC and is tracked separately from the `test` feature at https://github.com/rust-lang/rust/issues/64102. Let's reflect this in the feature gate. To avoid breaking all the benchmarks, libtest's `test::black_box` is a wrapping definition, not a reexport -- this means it is still under the `test` feature gate.