bpo-25172: Raise appropriate ImportError msg when crypt module used on Windows (GH-15149)

Lib/crypt.py

 """Wrapper to the POSIX crypt library call and associated functionality."""
 
-import _crypt
+import sys as _sys
+
+try:
+    import _crypt
+except ModuleNotFoundError:
+    if _sys.platform == 'win32':
+        raise ImportError("The crypt module is not supported on Windows")
+    else:
+        raise ImportError("The required _crypt module was not built as part of CPython")
+
 import string as _string
 from random import SystemRandom as _SystemRandom
 from collections import namedtuple as _namedtuple

Misc/NEWS.d/next/Windows/2019-08-06-18-09-18.bpo-25172.Akreij.rst

+Trying to import the :mod:`crypt` module on Windows will result in an :exc:`ImportError` with a message explaining that the module isn't supported on Windows. On other platforms, if the underlying ``_crypt`` module is not available, the ImportError will include a message explaining the problem.