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

Lib/crypt.py

@@ -1,6 +1,15 @@
 """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