ARROW-17975: [C++] Create at-fork facility

[pitrou]

Also migrate the ThreadPool class to use the new facility.

The util::GlobalForkSafeMutex facility is now unused, we may want to remove it in a later PR.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-17975

[pitrou]

@github-actions crossbow submit -g cpp

[github-actions]

Revision: 961a457

Submitted crossbow builds: ursacomputing/crossbow @ actions-21ee6e6b86

Task	Status
test-alpine-linux-cpp
test-build-cpp-fuzz
test-conda-cpp
test-conda-cpp-valgrind
test-cuda-cpp
test-debian-10-cpp-amd64
test-debian-10-cpp-i386
test-debian-11-cpp-amd64
test-debian-11-cpp-i386
test-fedora-35-cpp
test-ubuntu-18.04-cpp
test-ubuntu-18.04-cpp-release
test-ubuntu-18.04-cpp-static
test-ubuntu-20.04-cpp
test-ubuntu-20.04-cpp-20
test-ubuntu-20.04-cpp-bundled
test-ubuntu-20.04-cpp-thread-sanitizer
test-ubuntu-22.04-cpp

[westonpace]

Thanks for doing this. Looks like a very useful utility and IIRC the atfork handlers should be a safer way of solving this problem too.

[pitrou]

Yes, hopefully it should be more robust than the previous way of inspecting the current pid in random places...

[ursabot]

Benchmark runs are scheduled for baseline = 7f067f9 and contender = 619b034. 619b034 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Failed ⬇️1.69% ⬆️2.1%] test-mac-arm
[Failed ⬇️0.0% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️1.16% ⬆️0.74%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] 619b034b ec2-t3-xlarge-us-east-2
[Failed] 619b034b test-mac-arm
[Finished] 619b034b ursa-i9-9960x
[Finished] 619b034b ursa-thinkcentre-m75q
[Finished] 7f067f9a ec2-t3-xlarge-us-east-2
[Failed] 7f067f9a test-mac-arm
[Failed] 7f067f9a ursa-i9-9960x
[Finished] 7f067f9a ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java