posix: Replace DoubleForkAndExec() with ForkAndSpawn()

The DoubleForkAndExec() function was taking over 622 milliseconds to run
on macOS 11 (BigSur) on Intel i5-1038NG7. I did some debugging by adding
some custom traces and found that the fork() syscall is the bottleneck
here, i.e., the first fork() takes around 359 milliseconds and the
nested fork() takes around 263 milliseconds. Replacing the nested fork()
and exec() with posix_spawn() reduces the time consumption to 257
milliseconds!

See https://github.com/libuv/libuv/pull/3064 to know why fork() is so
slow on macOS and why posix_spawn() is a better replacement.

Another point to note is that even base::LaunchProcess() from Chromium
calls posix_spawnp() on macOS -
https://source.chromium.org/chromium/chromium/src/+/8f8d82dea0fa8f11f57c74dbb65126f8daba58f7:base/process/launch_mac.cc;l=295-296

Change-Id: I25c6ee9629a1ae5d0c32b361b56a1ce0b4b0fd26
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/3641386
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Mark Mentovai <mark@chromium.org>
8 files changed
tree: 6eb969d59750d520eae7412815a192dde1af8b57
  1. build/
  2. client/
  3. compat/
  4. doc/
  5. handler/
  6. infra/
  7. minidump/
  8. snapshot/
  9. test/
  10. third_party/
  11. tools/
  12. util/
  13. .clang-format
  14. .gitattributes
  15. .gitignore
  16. .gn
  17. .style.yapf
  18. .vpython
  19. .vpython3
  20. AUTHORS
  21. BUILD.gn
  22. codereview.settings
  23. CONTRIBUTORS
  24. DEPS
  25. LICENSE
  26. navbar.md
  27. package.h
  28. README.md
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