go/types: disable example on darwin/arm

Sadly examples cannot use the new internal/testenv, so this is
extends the crude build tag restriction in this file.

Change-Id: I49646ca71e45074a917813ae8e612cc715c78be8
Reviewed-on: https://go-review.googlesource.com/11086
Reviewed-by: Robert Griesemer <[email protected]>

Author: crawshaw

src/go/types/example_test.go

@@ -5,7 +5,7 @@
 // Only run where builders (build.golang.org) have
 // access to compiled packages for import.
 //
-// +build !arm64,!nacl
+// +build !arm,!arm64,!nacl
 
 package types_test