unix: skip failing test on freebsd-386

Updates golang/go#15186

Change-Id: I02403cbc9b3f1c786ee8093e1480edff891ecf13
Reviewed-on: https://go-review.googlesource.com/21676Reviewed-by: Andrew Gerrand <adg@golang.org>

unix/syscall_freebsd_test.go

@@ -7,6 +7,7 @@
 package unix_test
 
 import (
+	"os"
 	"testing"
 
 	"golang.org/x/sys/unix"
@@ -15,6 +16,9 @@ import (
 func TestSysctUint64(t *testing.T) {
 	_, err := unix.SysctlUint64("vm.max_kernel_address")
 	if err != nil {
+		if os.Getenv("GO_BUILDER_NAME") == "freebsd-386-gce101" {
+			t.Skipf("Ignoring known failing test (golang.org/issue/15186). Failed with: %v", err)
+		}
 		t.Fatal(err)
 	}
 }