Add C++17 std::not_fn negator.

Summary:
Exactly what it sounds like.

I plan to commit this in a couple of days assuming no objections.

Reviewers: mclow.lists, EricWF

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20799

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@271464 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed