Update NaCl SDK build for new location of irt_ppapi.h header file

This file is being added to the Chromium repo and removed from the NaCl repo.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3787
TEST=NaCl SDK trybots
R=binji@chromium.org, bradnelson@google.com

Review URL: https://codereview.chromium.org/164323003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251230 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251230