cmd/internal/gc: fix race build

Change-Id: Iab3f5538c135a21e071789e2c7b445b0a04a2ad0
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/8461
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/gc/racewalk.go

@@ -219,7 +219,8 @@ func racewalknode(np **Node, init **NodeList, wr int, skip int) {
 		OPLUS,
 		OREAL,
 		OIMAG,
-		OCOM:
+		OCOM,
+		OSQRT:
 		racewalknode(&n.Left, init, wr, 0)
 		goto ret