[libcxx] [www] Change http://cplusplus.github.io/LWG/lwg-defects.html# to https://wg21.link/lwg .

Fixes D37318.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@312258 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed