message: custom-named-profiles: fix profile for custom build
  The profile returned for custom build should have the proper 'root'
  field value.
  This fixes test build_script::profile_and_opt_level_set_correctly.
diff: @@ -234,6 +234,7 @@ impl Profiles {
  /// times).
  pub fn get_profile_run_custom_build(&self, for_unit_profile: &Profile) -> Profile {
  let mut result = Profile::default();
  + result.root = for_unit_profile.root;
  result.debuginfo = for_unit_profile.debuginfo;
  result.opt_level = for_unit_profile.opt_level;
  result
  