[libcxx] [www] Semi-manually change http://www.open-std.org and http://isocpp.org papers to https://wg21.link .

Fixes D37318.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@312259 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed