Two test failures in Cygwin

[jaraco]

In 1bcd839, I restored the running of cygwin tests for distutils after I realized that the "rust compiler" limitation only needed to affect the "pytest-ruff" dependency, now excluded upstream.

However, re-enabling the tests revealed we've had a couple of regressions since tests were disabled.

________ TestMingw32CCompiler.test_customize_compiler_with_msvc_python _________

self = <distutils.tests.test_mingwccompiler.TestMingw32CCompiler object at 0x6ffffe1d04c0>

    def test_customize_compiler_with_msvc_python(self):
        from distutils.cygwinccompiler import Mingw32CCompiler
    
        # In case we have an MSVC Python build, but still want to use
        # Mingw32CCompiler, then customize_compiler() shouldn't fail at least.
        # https://github.com/pypa/setuptools/issues/4456
>       compiler = Mingw32CCompiler()

distutils/tests/test_mingwccompiler.py:54: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <distutils.cygwinccompiler.Mingw32CCompiler object at 0x6ffffde848b0>
verbose = False, dry_run = False, force = False

    def __init__(self, verbose=False, dry_run=False, force=False):
        super().__init__(verbose, dry_run, force)
    
        shared_option = "-shared"
    
        if is_cygwincc(self.cc):
>           raise CCompilerError('Cygwin gcc cannot be used with --compiler=mingw32')
E           distutils.errors.CCompilerError: Cygwin gcc cannot be used with --compiler=mingw32

distutils/cygwinccompiler.py:274: CCompilerError
______ [doctest] distutils.unixccompiler.UnixCCompiler.find_library_file _______
371         data to go on: GCC seems to prefer the shared library, so
372         assume that *all* Unix C compilers do,
373         ignoring even GCC's "-static" option.
374 
375         >>> compiler = UnixCCompiler()
376         >>> compiler._library_root = lambda dir: dir
377         >>> monkeypatch = getfixture('monkeypatch')
378         >>> monkeypatch.setattr(os.path, 'exists', lambda d: 'existing' in d)
379         >>> dirs = ('/foo/bar/missing', '/foo/bar/existing')
380         >>> compiler.find_library_file(dirs, 'abc').replace('\\', '/')
Expected:
    '/foo/bar/existing/libabc.dylib'
Got:
    '/foo/bar/existing/cygabc.dll'

/cygdrive/d/a/distutils/distutils/distutils/unixccompiler.py:380: DocTestFailure

@lazka Can you take a look and suggest fixes?

[lazka]

sure, I'll have a look

edit: I can reproduce both issues locally

[DWesl]

I added the second in #209, if you want the context

[lazka]

Sorry for the delay, I created #270