Add the fact that we anticipate switching to use (some subset of) C++11

Add the fact that we anticipate switching to use (some subset of) C++11
after the 3.4 release to the release notes. See the *lengthy* llvmdev
and cfe-dev threads on this subject. There will be more emails,
discussion and announcements, but I want to make noise in as many places
as I can to get everyone's concerns voiced and understood.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194183 91177308-0d34-0410-b5e6-96231b3b80d8