This patch allows llvm-dwarfutil to utilize accelerator tables

generation code from DWARFLinker. It adds command line option:

--build-accelerator [none,DWARF]
                        Build accelerator tables(default: none)
  =none - Do not build accelerators
  =DWARF - Build accelerator tables according to the resulting DWARF version
       DWARFv4: .debug_pubnames and .debug_pubtypes
       DWARFv5: .debug_names

Differential Revision: https://reviews.llvm.org/D139638