Fixing a -Wcast-qual warning in GCC. No functional changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214399 91177308-0d34-0410-b5e6-96231b3b80d8
Fixing an -Woverloaded-virtual warnings by exposing the hidden virtual function as well. No functional changes intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214400 91177308-0d34-0410-b5e6-96231b3b80d8