Add win_clang to CQ trybots.

infra/config/cq.cfg

@@ -21,5 +21,9 @@ verifiers {
       builders { name: "win_angle_x64_rel_ng" }
       builders { name: "win_angle_x64_dbg_ng" }
     }
+    buckets {
+      name: "master.tryserver.chromium.win"
+      builders { name: "win_clang" }
+    }
   }
 }