Emit vtables for an extern template class as available_externally, not as
linkonce_odr. Emit construction vtables as internal in this case, since the ABI
does not guarantee that they will be availble externally.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175330 91177308-0d34-0410-b5e6-96231b3b80d8