While working on #184 I found that CygwinCCompiler is never used. If it was used it should be failing with TypeError as there's something wrong with get_msvcr (it shouldn't be returning None, https://github.com/pypa/distutils/pull/184/files#r1008651830).

It uses UnixCCompiler instead while compiling on that platform.

$ python -c 'import distutils.ccompiler as a; print(a.new_compiler())'
<distutils.unixccompiler.UnixCCompiler object at 0x6ffffff07c10>

I think the below line should be changed to cygwin instead of unix to use the correct compiler classes. Not sure why it was set to unix though. (and the blame is 22 years old, so no idea e49a115)