Push DwarfDebug::constructScopeDIE down into DwarfCompileUnit

One of many steps to generalize subprogram emission to both the DWO and
non-DWO sections (to emit -gmlt-like data under fission). Once the
functions are pushed down into DwarfCompileUnit some of the data
structures will be pushed at least into DwarfFile so that they can be
unique per-file, allowing emission to both files independently.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219345 91177308-0d34-0410-b5e6-96231b3b80d8
DebugInfo: The rest of pushing DwarfDebug::constructScopeDIE down into DwarfCompileUnit

Funnily enough, I copied it, but didn't actually remove the original in
r219345. Let's do that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219346 91177308-0d34-0410-b5e6-96231b3b80d8
Remove dead call to getTypeToTransformTo. The result is
unused.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219347 91177308-0d34-0410-b5e6-96231b3b80d8
Sink and coalesce DwarfDebug.cpp::addSectionLabel and DwarfUnit::addSectionLabel down into DwarfCompileUnit::addSectionLabel

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219351 91177308-0d34-0410-b5e6-96231b3b80d8