No functional change. Pre-emptive refactoring before I start pushing
some of this subprogram creation down into DWARFCompileUnit so I can
build different subprograms in the skeleton unit from the dwo unit for
adding -gmlt-like data to the skeleton.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218713 91177308-0d34-0410-b5e6-96231b3b80d8