Add back-passwd.h to the mix

servers/slapd/back-passwd/back-passwd.h

+/* $OpenLDAP$ */
+#ifndef _BACK_PASSWD_H
+#define _BACK_PASSWD_H
+
+#include "external.h"
+
+LDAP_BEGIN_DECL
+
+extern ldap_pvt_thread_mutex_t passwd_mutex;
+
+LDAP_END_DECL
+
+#endif /* _BACK_PASSWD_H */