MDEV-10315 - Online ALTER TABLE may get stuck in tdc_remove_table

There was race condition between online ALTER TABLE and statements performing
TABLE_SHARE release without marking it flushed (e.g. in case of table cache
overflow, SET @@global.table_open_cache, manager thread purging table cache).

The reason was missing mysql_cond_broadcast().

sql/table_cache.cc

@@ -876,6 +876,8 @@ void tdc_release_share(TABLE_SHARE *share)
   }
   if (--share->tdc.ref_count)
   {
+    if (!share->is_view)
+      mysql_cond_broadcast(&share->tdc.COND_release);
     mysql_mutex_unlock(&share->tdc.LOCK_table_share);
     mysql_mutex_unlock(&LOCK_unused_shares);
     DBUG_VOID_RETURN;