* Acquires write lock of the read/write lock `rwlock'. If the `rwlock'
* is locked by a writer or a reader the current thread will block until
* the other thread(s) have issued silc_rwlock_unlock for the `rwlock'.
* Acquires write lock of the read/write lock `rwlock'. If the `rwlock'
* is locked by a writer or a reader the current thread will block until
* the other thread(s) have issued silc_rwlock_unlock for the `rwlock'.