message: Keep unstable target features for asm feature checking
  Inline assembly uses the target features to determine which registers
  are available on the current target. However it needs to be able to
  access unstable target features for this.
  Fixes
diff: @@ -167,7 +167,7 @@ fn init(&self, sess: &Session) {
  }
  }
  - fn target_features(&self, _sess: &Session) -> Vec<rustc_span::Symbol> {
  + fn target_features(&self, _sess: &Session, _allow_unstable: bool) -> Vec<rustc_span::Symbol> {
  vec![]
  }
  