Use standard helper to skip Windows for /common

test/test_common.py

@@ -11,10 +11,10 @@ import pqclean
 import helpers
 
 
+@helpers.skip_windows()
 def test_common():
-    if os.name != 'nt':                    # Cannot build on Windows at the moment
     for d in os.listdir('common'):
-            primitive = re.sub("\.c$", "", d)        
+        primitive = re.sub(r"\.c$", "", d)
         binname = os.path.join('..', 'bin', 'test_'+primitive)
         helpers.make(binname)
         helpers.run_subprocess(binname)