As suggested on PR33912.
Trying to keep this small to make it easy to merge to the 5.0 branch. We can do a follow-up with more thorough renaming (diagnostic text, options, ids, etc.) later.
(For c++14 this was done in r215982, and I think a smaller patch for the 3.5 branch: http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20140818/113013.html)