Fix for x64. __unused is #defined elsewhere.
Recent versions of NDK do not define __off64_t, changed to int64_t.

BUG=346626
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/219483003

git-svn-id: http://linux-syscall-support.googlecode.com/svn/trunk@25 829466d3-f3f5-3ae4-62ad-de35cf9bba21