[llvm] [llvm][DWARFLinker] Fix gcc 13 -Wuninitialized warnings (PR #143867)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo approved this pull request.

The change LGTM, but it'd be nice to quote the actual warning message being fixed - as when reviewing the patch on its own, I can't figure out what the compiler could have warned about before.

https://github.com/llvm/llvm-project/pull/143867