Units: add test using GNU extension regex pattern, i.e. \s, \w

[hirooih]

dd177c3 just copy regex tests.
fc71cc9 uses GNU extension regex patterns.

Some changes are not equivalent with original to try more use of extensions.

[masatake]

If you rebase your changes on the latest HEAD of the master branch, the failures on centos6 will be fixed.

[masatake]

These test cases can be used for testing p/pcre2 regex flags.

[codecov]

Codecov Report

Merging #3035 (5938134) into master (41d7384) will not change coverage.
The diff coverage is n/a.

❗ Current head 5938134 differs from pull request most recent head 5ebfcc9. Consider uploading reports for the commit 5ebfcc9 to get more accurate results

@@           Coverage Diff           @@
##           master    #3035   +/-   ##
=======================================
  Coverage   87.35%   87.35%           
=======================================
  Files         200      200           
  Lines       47799    47799           
=======================================
  Hits        41756    41756           
  Misses       6043     6043           

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