[C++11] Update the coding standards to provide some important guidance

[C++11] Update the coding standards to provide some important guidance
about a few constructs in C++11 that are worth starting off in
a consistent manner within the codebase.

This will be matched with a change to clang-format's LLVM style which
will switch the options to support C++11 and use these conventions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202620 91177308-0d34-0410-b5e6-96231b3b80d8