Add the DW_AT_GNU_addr_base for the skeleton cu. Add support for
emitting the dwarf32 version of DW_FORM_sec_offset and correct
disassembler support.
Fix the assembly and dissassembly of DW_FORM_sec_offset. Found this by
changing both the string of the dwo_name to be correct and the type of
the statement list.

Testcases all around.