[BOLT][DWARF] Fix adding DW_AT_GNU_ranges_base

There are cases in DWARF4 when Skeleton CU has ranges, but dwo CU doesn't.
Bug was introduced in new DWARFRewriter where for DWARF4 it would fall through
to DWARF5 case.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D155033