go/types: fix suspect or

In https://go-review.googlesource.com/#/c/8611/ , these tests were
supposed to be skipped only for linux and darwin, as the comment says.
This patch fixes the logic in the if test.

Change-Id: Iff0a32186267457a414912c4c3ee4495650891a2
Reviewed-on: https://go-review.googlesource.com/12517Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>

src/go/types/stdlib_test.go

@@ -129,7 +129,7 @@ func TestStdTest(t *testing.T) {
 
 	// test/recover4.go is only built for Linux and Darwin.
 	// TODO(gri) Remove once tests consider +build tags (issue 10370).
-	if runtime.GOOS != "linux" || runtime.GOOS != "darwin" {
+	if runtime.GOOS != "linux" && runtime.GOOS != "darwin" {
 		return
 	}