Pass a 'ForVTable' flag to GetAddrOfThunk and pass it along to GetOrCreateLLVMFunction so that we

won't assert when building a thunk for an implicit virtual member function that is not marked used.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124967 91177308-0d34-0410-b5e6-96231b3b80d8