DwarfDebug: Include type units in accelerator tables.

Since type units aren't in the CUMap, use the DwarfUnits list to iterate
over units for tasks such as accelerator table building.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195776 91177308-0d34-0410-b5e6-96231b3b80d8