Reapply part of r237975, "Fix Clang -Wmissing-override warning", except for DIContext.h, to apease g++-4.7.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238012 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed