These methods rely on the current objfile to create types based on it.
Since dwarf2_per_cu_data is to become objfile-independent, these methods
need to mvoe.
int_type can be in dwarf2_per_objfile, as it only requires knowing about
the objfile.
addr_sized_int_type and addr_type also need to know about the DWARF
address type size, which is CU-specific. The dwarf2_cu objects seems
like a good place for it, as it knows both about the current objfile and
the current CU.