[sanitizer_common] [Darwin] Replace pty with pipe on posix_spawn path for spawning symbolizer (#170809)

Due to a legacy incompatibility with `atos`, we were allocating a pty
whenever we spawned the symbolizer. This is no longer necessary and we
can use a regular ol' pipe.

This PR is split into two commits:
- The first removes the pty allocation and replaces it with a pipe. This
relocates the `CreateTwoHighNumberedPipes` call to be common to the
`posix_spawn` and `StartSubprocess` path.
- The second commit adds the `child_stdin_fd_` field to
`SymbolizerProcess`, storing the read end of the stdin pipe. By holding
on to this fd for the lifetime of the symbolizer, we are able to avoid
getting SIGPIPE (which would occur when we write to a pipe whose
read-end had been closed due to the death of the symbolizer). This will
be very close to solving #120915, but this PR is intentionally not
touching the non-posix_spawn path.

rdar://165894284
5 files changed
tree: 440cb18faf00ba5b060c799b91bc093eab7f3595
  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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