Summary:
An implementation of std::experimental::propagate_const from Library Fundamentals Technical Specification v2.
No tests are provided for disallowed types like fancy pointers or function pointers as no code was written to handle these.
Reviewers: EricWF, mclow.lists
Differential Revision: http://reviews.llvm.org/D12486
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@273122 91177308-0d34-0410-b5e6-96231b3b80d8
