Added test [#CLICKHOUSE-31].

dbms/tests/queries/0_stateless/00466_comments_in_keyword.reference

+1
+1
+1
+1

dbms/tests/queries/0_stateless/00466_comments_in_keyword.sql

+SELECT 1 AS x ORDER/* hello */BY x;
+
+SELECT 1 AS x GROUP -- hello
+BY x;
+
+SELECT 1 AS x
+UNION/**/ALL
+SELECT 1;