Only use /W4 on Python 3.12 and newer

Author: vstinner

tests/setup.py

@@ -41,11 +41,17 @@
 else:
     # C compiler flags for MSVC
     COMMON_FLAGS.extend((
-        # Display warnings level 1 to 4
-        '/W4',
         # Treat all compiler warnings as compiler errors
         '/WX',
     ))
+    # Python 3.11 and older emits C4100 "unreferenced parameter" warnings
+    # on Py_UNUSED() parameters. Py_UNUSED() was modified in Python 3.12
+    # to support MSVC.
+    if sys.version_info >= (3, 12):
+        COMMON_FLAGS.extend((
+            # Display warnings level 1 to 4
+            '/W4',
+        ))
     CFLAGS = list(COMMON_FLAGS)
 CXXFLAGS = list(COMMON_FLAGS)