Fix PR22393. When recursively replacing an aggregate with a smaller

Fix PR22393. When recursively replacing an aggregate with a smaller
aggregate or scalar, the debug info needs to refer to the absolute offset
(relative to the entire variable) instead of storing the offset inside
the smaller aggregate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227702 91177308-0d34-0410-b5e6-96231b3b80d8