Integration test for CPU feature detection

[graebm]

Issue:
I accidentally committed broken CPU-feature-detection code in #1182 (fixed the next day by #1184)

This kind of accident slipped through because I was in a rush, and we don't have unit tests to double-check this particular code. Unit tests for feature detection are hard because these features vary wildly machine to machine.

Description of changes:
Add an integration test that checks CPU-feature-detection against linux's easy-to-parse /proc/cpuinfo.

This test is skipped on platforms like Windows and Apple where there's no simple way to query CPU features

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.27%. Comparing base (0e7637f) to head (4596003).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1186   +/-   ##
=======================================
  Coverage   84.27%   84.27%           
=======================================
  Files          57       57           
  Lines        5976     5976           
=======================================
  Hits         5036     5036           
  Misses        940      940           

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