gh-154200: Use sysconfig.get_platform() in test_importlib.test_windows

test_tagged_suffix computed its expected extension suffix with a vendored port of
distutils.util.get_platform() that sniffs sys.version for 'amd64'. Python/getversion.c
truncates the compiler segment of sys.version at 80 characters, so on clang-cl builds --
whose banner carries a long __clang_version__ -- the marker is cut off, the helper falls
through to sys.platform ('win32'), and the test expects '.cp316t-win32.pyd' while the
interpreter correctly reports '.cp316t-win_amd64.pyd'.

sysconfig.get_platform() no longer parses sys.version on Windows (gh-145410); it uses the
_sysconfig C accelerator, which derives the platform from compile-time architecture
macros and is compiler-agnostic. Use it and drop the vendored copy, its only caller.

This also removes the VSCMD_ARG_TGT_ARCH branch, which trusted the ambient Visual Studio
target architecture over the interpreter actually running the test.

Author: SynaptSea

Lib/test/test_importlib/test_windows.py

@@ -4,6 +4,7 @@
 import os
 import re
 import sys
+import sysconfig
 import unittest
 from test import support
 from test.support import import_helper
@@ -17,25 +18,6 @@
     EnumKey, CloseKey, DeleteKey, OpenKey
 )
 
-def get_platform():
-    # Port of distutils.util.get_platform().
-    TARGET_TO_PLAT = {
-            'x86' : 'win32',
-            'x64' : 'win-amd64',
-            'arm' : 'win-arm32',
-        }
-    if ('VSCMD_ARG_TGT_ARCH' in os.environ and
-        os.environ['VSCMD_ARG_TGT_ARCH'] in TARGET_TO_PLAT):
-        return TARGET_TO_PLAT[os.environ['VSCMD_ARG_TGT_ARCH']]
-    elif 'amd64' in sys.version.lower():
-        return 'win-amd64'
-    elif '(arm)' in sys.version.lower():
-        return 'win-arm32'
-    elif '(arm64)' in sys.version.lower():
-        return 'win-arm64'
-    else:
-        return sys.platform
-
 def delete_registry_tree(root, subkey):
     try:
         hkey = OpenKey(root, subkey, access=KEY_ALL_ACCESS)
@@ -143,7 +125,7 @@ def test_tagged_suffix(self):
         suffixes = self.machinery.EXTENSION_SUFFIXES
         abi_flags = "t" if support.Py_GIL_DISABLED else ""
         ver = sys.version_info
-        platform = re.sub('[^a-zA-Z0-9]', '_', get_platform())
+        platform = re.sub('[^a-zA-Z0-9]', '_', sysconfig.get_platform())
         expected_tag = f".cp{ver.major}{ver.minor}{abi_flags}-{platform}.pyd"
         try:
             untagged_i = suffixes.index(".pyd")