When we're emitting a constructor or destructor call from a delegating
constructor, retrieve our VTT parameter directly. Fixes PR14588 /
<rdar://problem/12867962>.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174042 91177308-0d34-0410-b5e6-96231b3b80d8