[C++] CMake fails on aarch64 systems that do not support -march=armv8-a+crc+crypto

[asfimport]

I was trying to build the project on a rockpro64 system to look into something else and ran into this

-- Arrow build warning level: PRODUCTION
CMake Error at cmake_modules/SetupCxxFlags.cmake:332 (message):
  Unsupported arch flag: -march=armv8-a+crc+crypto.
Call Stack (most recent call first):
  CMakeLists.txt:398 (include)

-- Configuring incomplete, errors occurred!

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

PRs and other links:

• GitHub Pull Request #6907

_{Note: This issue was originally created as ARROW-8410. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
cc @cyb70289

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 6907
#6907