Build the debuginfo node for a coroutine environment. It looks the same as the debuginfo for
an enum. See build_enum_type_di_node for more information.
Build the debuginfo node for an enum type. The listing below shows how such a
type looks like at the LLVM IR/DWARF level. It is a DW_TAG_structure_type
with a single DW_TAG_variant_part that in turn contains a DW_TAG_variant
for each variant of the enum. The variant-part also contains a single member
describing the discriminant, and a nested struct type for each of the variants.