[C++11] Add 'override' keywords and remove 'virtual'. Additionally add 'final' and leave 'virtual' on some methods that are marked virtual without overriding anything and have no obvious overrides themselves.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207511 91177308-0d34-0410-b5e6-96231b3b80d8
13 files changed