[libc++] Revert r363692 which implements P0608R3

The change caused a large number of compiler failures in
Google's codebase.  People need time to evaluate the impact.



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@363764 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed