[clang] [llvm] [LLVM][DWARF] Fix accelerator swtiching with TU re-use (PR #77511)

[Alexander Yermolovich via cfe-commits]

ayermolo wrote:

There is another bug on when we exit from addDwarfTypeUnitType. I need to construct a small repro for it.

https://github.com/llvm/llvm-project/pull/77511