Documentation tweaks: Fix a typo in a reference to the C++ standard,
another typo in a comment, and update formatting of some comments to
use Doxygen \brief annotations instead of repeating the name of the
documented entity.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194092 91177308-0d34-0410-b5e6-96231b3b80d8