compat BUGFIX define crypt_data if not available

Author: michalvasko

compat/compat.h.in

@@ -213,6 +213,12 @@ char *get_current_dir_name(void);
 #endif
 
 #ifndef HAVE_CRYPT_R
+
+/* unused anyway */
+struct crypt_data {
+    char a;
+};
+
 char *crypt_r(const char *phrase, const char *setting, struct crypt_data *data);
 #endif