[NaCl SDK] nacl_io: Add plumbing for new IRT interfaces.

This change adds newlib wrapping for the new IRT syscalls
that were added recently.  It also adds plubming for them
through to the kernel_proxy.

BUG=307572
R=noelallen@chromium.org

Review URL: https://codereview.chromium.org/26378007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229503 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229503