This generalizes the range handling for ranges in both the skeleton and
full unit, laying the foundation for the addition of more ranges (rather
than just the CU's special case) in the skeleton CU with fission+gmlt.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221202 91177308-0d34-0410-b5e6-96231b3b80d8