Simplify filter accepts function to just return 'condition' instead of branching to return true/false. No functional change.
Revert r198208 and reapply:

      r198196: Use a pointer to keep track of the skeleton unit for each normal unit and construct it up front.
      r198199: Reapply r198196 with a fix to zero initialize the skeleton pointer.
      r198202: Fix aranges and split dwarf by ensuring that the symbol and relocation back to the compile unit from the aranges section is to the skeleton unit and not the one in the dwo.

with a fix to use integer 0 for DW_AT_low_pc since the relocation to the text section symbol was causing issues with COFF. Accordingly remove addLocalLabelAddress and machinery since we're not currently using it.