Add Cygwin build

[sy-records]

Add Cgywin build at release time

[codecov]

Codecov Report

Merging #4222 (ac00ea0) into master (8ce5041) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4222      +/-   ##
==========================================
- Coverage   50.18%   50.15%   -0.03%     
==========================================
  Files          71       71              
  Lines       14268    14268              
==========================================
- Hits         7160     7156       -4     
- Misses       7108     7112       +4     

Impacted Files	Coverage Δ
src/protocol/base.cc	61.18% <0.00%> (-1.98%)	⬇️
src/core/channel.cc	70.87% <0.00%> (-0.98%)	⬇️

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[janreges]

Hi @sy-records - see my ticket #5189

Would it be possible to add cygwin build to the latest version 5.1.0 using the latest version of Cygwin? Or do you know of a reason that would prevent it?