closes bpo-38402: Check error of primitive crypt/crypt_r. (GH-16599)

Checks also for encryption algorithms methods not supported in different
OSs.

Signed-off-by: Antonio Gutierrez <chibby0ne@gmail.com>

Lib/crypt.py

@@ -10,6 +10,7 @@ except ModuleNotFoundError:
     else:
         raise ImportError("The required _crypt module was not built as part of CPython")
 
+import errno
 import string as _string
 from random import SystemRandom as _SystemRandom
 from collections import namedtuple as _namedtuple
@@ -88,7 +89,14 @@ def _add_method(name, *args, rounds=None):
     method = _Method(name, *args)
     globals()['METHOD_' + name] = method
     salt = mksalt(method, rounds=rounds)
-    result = crypt('', salt)
+    result = None
+    try:
+        result = crypt('', salt)
+    except OSError as e:
+        # Not all libc libraries support all encryption methods.
+        if e.errno == errno.EINVAL:
+            return False
+        raise
     if result and len(result) == method.total_size:
         methods.append(method)
         return True