message: Derive debug from `BuildTargetConfigValue`
diff: @@ -2222,6 +2222,7 @@ impl BuildTargetConfig {
  }
  /// Represents a value of `build.target`.
  +#[derive(Debug)]
  pub enum BuildTargetConfigValue<'a> {
  /// Path to a target specification file (in JSON).
  /// <https://doc.rust-lang.org/rustc/targets/custom.html>
  