Update C++17 status; mark issues 2170, 2377, and 2408 as complete. We already do these; no code changes necessary.
Update C++17 status; mark issues 2170, 2377, and 2408 as complete. We already do these; no code changes necessary.

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@235992 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx