os/exec: skip fork test on darwin/arm64

Just like darwin/arm.

Change-Id: Ia8c912e91259a5073aa3ab2b6509a18aa9a1fce7
Reviewed-on: https://go-review.googlesource.com/8818Reviewed-by: Minux Ma <minux@golang.org>

src/os/exec/exec_test.go

@@ -27,10 +27,12 @@ import (
 	"time"
 )
 
+// iOS cannot fork
+var iOS = runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64")
+
 func helperCommand(t *testing.T, s ...string) *exec.Cmd {
-	if runtime.GOOS == "nacl" || (runtime.GOOS == "darwin" && runtime.GOARCH == "arm") {
-		// iOS cannot fork
-		t.Skipf("skipping on %s/%s", runtime.GOOS, runtime.GOARCH)
+	if runtime.GOOS == "nacl" || iOS {
+		t.Skipf("skipping on %s/%s, cannot fork", runtime.GOOS, runtime.GOARCH)
 	}
 	cs := []string{"-test.run=TestHelperProcess", "--"}
 	cs = append(cs, s...)
@@ -50,8 +52,8 @@ func TestEcho(t *testing.T) {
 }
 
 func TestCommandRelativeName(t *testing.T) {
-	if runtime.GOOS == "darwin" && runtime.GOARCH == "arm" {
-		t.Skip("skipping on darwin/arm")
+	if iOS {
+		t.Skip("skipping on darwin/%s, cannot fork", runtime.GOARCH)
 	}
 
 	// Run our own binary as a relative path
@@ -428,10 +430,9 @@ func TestExtraFiles(t *testing.T) {
 	switch runtime.GOOS {
 	case "nacl", "windows":
 		t.Skipf("skipping test on %q", runtime.GOOS)
-	case "darwin":
-		if runtime.GOARCH == "arm" {
-			t.Skipf("skipping test on %s/%s", runtime.GOOS, runtime.GOARCH)
-		}
+	}
+	if iOS {
+		t.Skipf("skipping test on %s/%s, cannot fork", runtime.GOOS, runtime.GOARCH)
 	}
 
 	// Ensure that file descriptors have not already been leaked into