Add named posix semaphore lifetime operations on linux (#192278)

This implements the second part of #190847 

Specifically, this pr adds `sem_open`, `sem_close`, and `sem_unlink` for
posix semaphore on linux.
https://pubs.opengroup.org/onlinepubs/9799919799/functions/sem_open.html

https://pubs.opengroup.org/onlinepubs/9799919799/functions/sem_close.html

https://pubs.opengroup.org/onlinepubs/9799919799/functions/sem_unlink.html

Since it targets on linux implementation, two extra things are added:
1. add system call wrappers for `mmap`, `munmap`, `link`, `unlink`, and
`ftruncate`. Those are necessary for the implementation of semaphore on
linux. Wrappers is added based on the refactor proposal:
https://libc.llvm.org/dev/syscall_wrapper_refactor.html.
2. refactor the previous semaphore implementation, put it under `linux/`
since its based on linux.
13 files changed
tree: 63c5a83f554869180a09a96b5e0bba3ad5ccfb69
  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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