message: Change name of "dataful" variant to "untagged"
  This is in anticipation of a new enum layout, in which the niche
  optimization may be applied even when multiple variants have data.
diff: @@ -42,10 +42,10 @@ pub(crate) fn codegen_set_discriminant<'tcx>(
  Variants::Multiple {
  tag: _,
  tag_field,
  - tag_encoding: TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start },
  + tag_encoding: TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start },
  variants: _,
  } => {
  - if variant_index != dataful_variant {
  + if variant_index != untagged_variant {
  let niche = place.place_field(fx, mir::Field::new(tag_field));
  let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
  let niche_value = ty::ScalarInt::try_from_uint(
  @@ -113,7 +113,7 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
  let res = CValue::by_val(val, dest_layout);
  dest.write_cvalue(fx, res);
  }
  - TagEncoding::Niche { dataful_variant, ref niche_variants, niche_start } => {
  + TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
  // Rebase from niche values to discriminants, and check
  // whether the result is in range for the niche variants.
  @@ -169,8 +169,9 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
  fx.bcx.ins().iadd_imm(relative_discr, i64::from(niche_variants.start().as_u32()))
  };
  - let dataful_variant = fx.bcx.ins().iconst(cast_to, i64::from(dataful_variant.as_u32()));
  - let discr = fx.bcx.ins().select(is_niche, niche_discr, dataful_variant);
  + let untagged_variant =
  + fx.bcx.ins().iconst(cast_to, i64::from(untagged_variant.as_u32()));
  + let discr = fx.bcx.ins().select(is_niche, niche_discr, untagged_variant);
  let res = CValue::by_val(discr, dest_layout);
  dest.write_cvalue(fx, res);
  }
  