[dev.regabi] cmd/compile: use node walked flag to prevent double walk for walkSwitch

CL 283672 added a flag to prevent double walking, use that flag instead
of checking SwitchStmt.Compiled field.

Passes toolstash -cmp.

Change-Id: Idb8f9078412fb789f51ed4fc4206638011e38a93
Reviewed-on: https://go-review.googlesource.com/c/go/+/283733
Trust: Cuong Manh Le <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>

Author: cuonglm

src/cmd/compile/internal/walk/switch.go

@@ -19,9 +19,10 @@ import (
 // walkSwitch walks a switch statement.
 func walkSwitch(sw *ir.SwitchStmt) {
 	// Guard against double walk, see #25776.
-	if len(sw.Cases) == 0 && len(sw.Compiled) > 0 {
+	if sw.Walked() {
 		return // Was fatal, but eliminating every possible source of double-walking is hard
 	}
+	sw.SetWalked(true)
 
 	if sw.Tag != nil && sw.Tag.Op() == ir.OTYPESW {
 		walkSwitchType(sw)