handle openmp deprecation

[TimTaylor]

Building locally I saw the the following warning:

fread.c:2479:15: warning: ‘master’ construct deprecated since OpenMP 5.1, use ‘masked’ [-Wdeprecated-openmp]

Link to relevant documentation:
https://www.openmp.org/spec-html/5.1/openmpse16.html

Note I'm unsure on the potential use of the filter clause so it is probably worth digging in to a little first.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.01%. Comparing base (813ed95) to head (9efd5de).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7882   +/-   ##
=======================================
  Coverage   99.01%   99.01%           
=======================================
  Files          88       88           
  Lines       17309    17309           
=======================================
  Hits        17139    17139           
  Misses        170      170           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.