runtime: skip fork test on darwin/arm64

Just like darwin/arm.

Change-Id: Ie4998d24b2d891a9f6c8047ec40cd3fdf80622cd
Reviewed-on: https://go-review.googlesource.com/8812
Reviewed-by: Minux Ma <minux@golang.org>
diff --git a/src/runtime/crash_test.go b/src/runtime/crash_test.go
index 7bb3d28..975defd 100644
--- a/src/runtime/crash_test.go
+++ b/src/runtime/crash_test.go
@@ -42,8 +42,9 @@
 	case "android", "nacl":
 		t.Skipf("skipping on %s", runtime.GOOS)
 	case "darwin":
-		if runtime.GOARCH == "arm" {
-			t.Skipf("skipping on %s/%s", runtime.GOOS, runtime.GOARCH)
+		switch runtime.GOARCH {
+		case "arm", "arm64":
+			t.Skipf("skipping on %s/%s, no fork", runtime.GOOS, runtime.GOARCH)
 		}
 	}