bpo-40280: Use presence of msvcrt module to detect Windows (GH-30930)

Lib/subprocess.py

@@ -65,10 +65,15 @@
            # NOTE: We intentionally exclude list2cmdline as it is
            # considered an internal implementation detail.  issue10838.
 
-_mswindows = sys.platform == "win32"
+# use presence of msvcrt to detect Windows-like platforms (see bpo-8110)
+try:
+    import msvcrt
+except ModuleNotFoundError:
+    _mswindows = False
+else:
+    _mswindows = True
 
 if _mswindows:
-    import msvcrt
     import _winapi
     from _winapi import (CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP,
                          STD_INPUT_HANDLE, STD_OUTPUT_HANDLE,

Misc/NEWS.d/next/Library/2022-01-16-14-07-14.bpo-40280.LtFHfF.rst

@@ -1,4 +1,4 @@
 :mod:`subprocess` now imports Windows-specific imports when
-``sys.platform == "win32"`` and POSIX-specific imports on all other
+``msvcrt`` module is available, and POSIX-specific imports on all other
 platforms. This gives a clean exception when ``_posixsubprocess`` is not
-available (e.g. Emscripten browser target) and it's slightly faster, too.
+available (e.g. Emscripten browser target).