C++11: Document some limitations imposed by MSVC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206480 91177308-0d34-0410-b5e6-96231b3b80d8
C++11: Compatibility with (C++03 => MSVC)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206481 91177308-0d34-0410-b5e6-96231b3b80d8