ARROW-14301: [C++] use consistent CMAKE_CXX_STANDARD definition

[coryan]

Tested locally with

archery docker run -e SETUPTOOLS_SCM_PRETEND_VERSION="6.0.0.dev444" -e CMAKE_ARGS=-DCMAKE_CXX_STANDARD=17 ubuntu-cpp

and

archery docker run -e SETUPTOOLS_SCM_PRETEND_VERSION="6.0.0.dev444" -e CMAKE_ARGS=-DCMAKE_CXX_STANDARD=11 ubuntu-cpp

and

archery docker run -e SETUPTOOLS_SCM_PRETEND_VERSION="6.0.0.dev444"  ubuntu-cpp

[github-actions]

https://issues.apache.org/jira/browse/ARROW-14301

[pitrou]

@github-actions crossbow submit -g cpp

[github-actions]

Revision: cd105f5

Submitted crossbow builds: ursacomputing/crossbow @ actions-920

Task	Status
test-conda-cpp
test-conda-cpp-valgrind
test-debian-11-cpp
test-fedora-33-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-14
test-ubuntu-20.04-cpp-17
test-ubuntu-20.04-cpp-thread-sanitizer

[kou]

+1

Failures are unrelated.

[ursabot]

Benchmark runs are scheduled for baseline = 0fbd5e4 and contender = 7bc63c0. 7bc63c0 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
[Finished ⬇️0.68% ⬆️0.0%] ursa-i9-9960x
[Failed ⬇️0.0% ⬆️0.0%] ursa-thinkcentre-m75q
Supported benchmarks:
ursa-i9-9960x: langs = Python, R, JavaScript
ursa-thinkcentre-m75q: langs = C++, Java
ec2-t3-xlarge-us-east-2: cloud = True