Function build_discr_member_di_node

fn build_discr_member_di_node<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    enum_or_coroutine_type_and_layout: TyAndLayout<'tcx>,
    enum_or_coroutine_type_di_node: &'ll DIType,
) -> Option<&'ll DIType>

Builds the DW_TAG_member describing where we can find the tag of an enum. Returns None if the enum does not have a tag.

      DW_TAG_structure_type              (top-level type for enum)
        DW_TAG_variant_part              (variant part)
          DW_AT_discr                    (reference to discriminant DW_TAG_member)
--->      DW_TAG_member                  (discriminant member)
          DW_TAG_variant                 (variant 1)
          DW_TAG_variant                 (variant 2)
          DW_TAG_variant                 (variant 3)
        DW_TAG_structure_type            (type of variant 1)
        DW_TAG_structure_type            (type of variant 2)
        DW_TAG_structure_type            (type of variant 3)