LibC: Move crypt() and crypt_r() to the right header file

According to POSIX.1 these should be in <crypt.h>.

Userland/Libraries/LibCrypt/crypt.cpp

@@ -6,8 +6,9 @@
 #include <AK/Base64.h>
 #include <AK/Types.h>
 #include <LibCrypto/Hash/SHA2.h>
+#include <crypt.h>
+#include <errno.h>
 #include <string.h>
-#include <unistd.h>
 
 extern "C" {
 

Userland/Libraries/LibCrypt/crypt.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+/* standard symbolic constants and types
+ *
+ * values from POSIX standard unix specification
+ *
+ * https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/unistd.h.html
+ */
+
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+struct crypt_data {
+    int initialized;
+    char result[65];
+};
+
+char* crypt(const char* key, const char* salt);
+char* crypt_r(const char* key, const char* salt, struct crypt_data* data);
+
+__END_DECLS