From Android release M (Marshmallow), hard linking files is blocked
and an attempt to call link() on a file will return EACCES.
- https://code.google.com/p/android-developer-preview/issues/detail?id=3150

Change-Id: Ifdadaa31e3d5ee330553f45db6c001897dc955be
Reviewed-on: https://go-review.googlesource.com/17339Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>