cmd/dist: detect gohostarch on ios/arm64

Add a case for gohostos == "ios" along with "darwin".

Updates #38485.

Change-Id: Ic7310e6c97d405f78a5e5db1a639860455e61327
Reviewed-on: https://go-review.googlesource.com/c/go/+/259337
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

src/cmd/dist/main.go

@@ -129,7 +129,7 @@ func main() {
 			gohostarch = "riscv64"
 		case strings.Contains(out, "s390x"):
 			gohostarch = "s390x"
-		case gohostos == "darwin":
+		case gohostos == "darwin", gohostos == "ios":
 			if strings.Contains(run("", CheckExit, "uname", "-v"), "RELEASE_ARM64_") {
 				gohostarch = "arm64"
 			}