[lldb][SymbolFileDWARF] Ignore Declaration when searching through UniqueDWARFASTTypeList in C++ (#120809)

This addresses an issue encountered when investigating
https://github.com/llvm/llvm-project/pull/120569.

In `ParseTypeFromDWARF`, we insert the parsed type into
`UniqueDWARFASTTypeMap` using the typename and `Declaration` obtained
with `GetUniqueTypeNameAndDeclaration`. For C++
`GetUniqueTypeNameAndDeclaration` will zero the `Declaration` info
(presumably because forward declaration may not have it, and for C++,
ODR means we can rely on fully qualified typenames for uniqueing). When
we then called `CompleteType`, we would first `MapDeclDIEToDefDIE`,
updating the `UniqueDWARFASTType` we inserted previously with the
`Declaration` of the definition DIE (without zeroing it). We would then
call into `ParseTypeFromDWARF` for the same type again, and search the
`UniqueDWARFASTTypeMap`. But we do the search using a zeroed declaration
we get from `GetUniqueTypeNameAndDeclaration`.

This particular example was fixed by
https://github.com/llvm/llvm-project/pull/120569 but this still feels a
little inconsistent. I'm not entirely sure we can get into that
situation after that patch anymore. So the only test-case I could come
up with was the unit-test which calls `MapDeclDIEToDefDIE` directly.
2 files changed
tree: b25cfe1574226cc3b6824a59baf56af3645e5a28
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. libc/
  11. libclc/
  12. libcxx/
  13. libcxxabi/
  14. libunwind/
  15. lld/
  16. lldb/
  17. llvm/
  18. llvm-libgcc/
  19. mlir/
  20. offload/
  21. openmp/
  22. polly/
  23. pstl/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-tidy
  29. .git-blame-ignore-revs
  30. .gitattributes
  31. .gitignore
  32. .mailmap
  33. CODE_OF_CONDUCT.md
  34. CONTRIBUTING.md
  35. LICENSE.TXT
  36. pyproject.toml
  37. README.md
  38. SECURITY.md
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