Reland "[ORC] Track __emutls_t definitions in IRMaterializationUnit" (#207161) (#208413)

Relands #207161, which was reverted in #207775 after the new
`clang/test/Interpreter/emulated-tls.cpp` failed on Darwin with `Symbols
not found: [ ___emutls_get_address ]`.

The `IRMaterializationUnit` fix and the test are unchanged from #207161.
What the failure exposed is that thread_locals never worked in
clang-repl on Darwin: `__emutls_get_address` is implemented in the
compiler-rt builtins static archive, and nothing links it into the
process, so process-symbol lookup cannot resolve it (on Linux it
resolves from `libgcc_s.so`).

New in this reland, per @lhames's suggestion (option 2) on the original
PR:

- `clang/lib/Interpreter/IncrementalExecutor.cpp`: on `__APPLE__`,
reference `__emutls_get_address` (forcing the builtins archive member to
be linked in) and define it as an absolute symbol in the process-symbols
JITDylib, following the precedent of the MinGW `__main` workaround in
`lli.cpp`. Scoped to the default in-process JITBuilder path only — the
host address would be meaningless for an out-of-process executor, and
custom-builder clients do their own setup.

Verified on an aarch64-darwin machine: the previously failing test now
passes, along with the rest of `clang/test/Interpreter`.

@vgvassilev @lhames — could you take a look?

🤖 Done with the help of [Claude Code](https://claude.com/claude-code)
(Claude Opus 4.8, human in the loop)

Co-authored-by: Emery Conrad <emery.conrad@chicagotrading.com>
3 files changed
tree: c7b8af78709f0094dba106a4128ea7aad8f6f0fe
  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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