[libclang] Add a test to make sure annotation works fine in the presence of
'override' on the method.

This was fixed in a previous commit, generally handling attributes that are at the
end of the declaration.

rdar://13140589

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174734 91177308-0d34-0410-b5e6-96231b3b80d8