Make test_customize_compiler run on mingw

Simply, run it for the subclasses for `UnixCCompiler`

Author: naveen521kk

distutils/tests/test_sysconfig.py

@@ -12,7 +12,7 @@
 
 import distutils
 from distutils import sysconfig
-from distutils.ccompiler import get_default_compiler  # noqa: F401
+from distutils.ccompiler import new_compiler  # noqa: F401
 from distutils.unixccompiler import UnixCCompiler
 from test.support import swap_item
 
@@ -109,7 +109,7 @@ def set_executables(self, **kw):
 
         return comp
 
-    @pytest.mark.skipif("get_default_compiler() != 'unix'")
+    @pytest.mark.skipif("not isinstance(new_compiler(), UnixCCompiler)")
     def test_customize_compiler(self):
         # Make sure that sysconfig._config_vars is initialized
         sysconfig.get_config_vars()