os/exec: skip unsupported test on Android

The underlying system call tested by TestCredentialNoSetGroups
is blocked on Android.

Discovered while running all.bash from an Android device; the syscall
is only blocked in an app context.

Change-Id: I16fd2e64636a0958b0ec86820723c0577b8f8f24
Reviewed-on: https://go-review.googlesource.com/c/go/+/170945
Run-TryBot: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/exec/exec_posix_test.go

@@ -8,6 +8,7 @@ package exec_test
 
 import (
 	"os/user"
+	"runtime"
 	"strconv"
 	"syscall"
 	"testing"
@@ -15,6 +16,10 @@ import (
 )
 
 func TestCredentialNoSetGroups(t *testing.T) {
+	if runtime.GOOS == "android" {
+		t.Skip("unsupported on Android")
+	}
+
 	u, err := user.Current()
 	if err != nil {
 		t.Fatalf("error getting current user: %v", err)