Fixed #5167: test_customize_compiler does not apply under non unix compilers

tests/test_sysconfig.py

 """Tests for distutils.dist."""
 
 from distutils import sysconfig
+from distutils.ccompiler import get_default_compiler
+
 import os
 import unittest
 
@@ -41,6 +43,10 @@ class SysconfigTestCase(unittest.TestCase):
 
     def test_customize_compiler(self):
 
+        # not testing if default compiler is not unix
+        if get_default_compiler() != 'unix':
+            return
+
         os.environ['AR'] = 'xxx'
 
         # make sure AR gets caught