gh-149879: Don't import msvcrt in _pyio on Cygwin (#149899)

The msvcrt extension module cannot be built on Cygwin.

Lib/_pyio.py

@@ -10,7 +10,7 @@
 import sys
 # Import _thread instead of threading to reduce startup cost
 from _thread import allocate_lock as Lock
-if sys.platform in {'win32', 'cygwin'}:
+if sys.platform == 'win32':
     from msvcrt import setmode as _setmode
 else:
     _setmode = None