[C++11] Add 'override' keyword to virtual methods that override their base class.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@203758 91177308-0d34-0410-b5e6-96231b3b80d8
Remove unreachable PragmaCaptured method. It's not a real PPCallback.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@203759 91177308-0d34-0410-b5e6-96231b3b80d8