[clang][DebugInfo] Emit unified (Itanium) mangled name to structor declarations (#154142)

Depends on https://github.com/llvm/llvm-project/pull/154137

This patch is motivated by
https://github.com/llvm/llvm-project/pull/149827, where we plan on using
mangled names on structor declarations to find the exact structor
definition that LLDB's expression evaluator should call.

Given a `DW_TAG_subprogram` for a function declaration, the most
convenient way for a debugger to find the corresponding definition is to
use the `DW_AT_linkage_name` (i.e., the mangled name). However, we
currently can't do that for constructors/destructors because Clang
doesn't attach linkage names to them. This is because, depending on ABI,
there can be multiple definitions for a single constructor/destructor
declaration. The way GCC works around this is by producing a `C4`/`D4`
"unified" mangling for structor declarations (see
[godbolt](https://godbolt.org/z/Wds6cja9K)). GDB uses this to locate the
relevant definitions.

This patch aligns Clang with GCC's DWARF output and allows us to
implement the same lookup scheme in LLDB.
15 files changed
tree: c92d62f544fabd76dffb93ea91cf3bed60d3c220
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libsycl/
  16. libunwind/
  17. lld/
  18. lldb/
  19. llvm/
  20. llvm-libgcc/
  21. mlir/
  22. offload/
  23. openmp/
  24. orc-rt/
  25. polly/
  26. runtimes/
  27. third-party/
  28. utils/
  29. .clang-format
  30. .clang-format-ignore
  31. .clang-tidy
  32. .git-blame-ignore-revs
  33. .gitattributes
  34. .gitignore
  35. .mailmap
  36. CODE_OF_CONDUCT.md
  37. CONTRIBUTING.md
  38. LICENSE.TXT
  39. pyproject.toml
  40. README.md
  41. SECURITY.md
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