Linux 5.0 (commit 231baecdef7a) renames CRYPTO_TFM_REQ_WEAK_KEY to
CRYPTO_TFM_REQ_FORBID_WEAK_KEYS.

--- a/libcfs/libcfs/crypto/llcrypt_private.h
+++ b/libcfs/libcfs/crypto/llcrypt_private.h
@@ -15,6 +15,10 @@
 #include <crypto/hash.h>
 #include <lustre_disk.h>
 
+#ifndef CRYPTO_TFM_REQ_FORBID_WEAK_KEYS
+#define CRYPTO_TFM_REQ_FORBID_WEAK_KEYS CRYPTO_TFM_REQ_WEAK_KEY
+#endif
+
 #define CONST_STRLEN(str)	(sizeof(str) - 1)
 
 #define FS_KEY_DERIVATION_NONCE_SIZE	16