[dev.regabi] cmd/compile: use node walked flag to prevent double walk for walkSwitch
[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 <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
Run-TryBot: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>

nawawi/go,golang/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go,cloudflare/go,cloudflare/go,cloudflare/go,golang/go