Fix PR19408 - Missing static this adjustment in a vtordisp thunk

Also fix a few other vtordisp-related bugs.

Reviewed at http://reviews.llvm.org/D3400

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206457 91177308-0d34-0410-b5e6-96231b3b80d8