Do not set the live address of a const result child if its parent has an invalid live address

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@224142 91177308-0d34-0410-b5e6-96231b3b80d8
Do attempt to ask the impl_backend for the live address of a const result if none is stored in the object itself; this is for symmetry with GetAddressOf()

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@224143 91177308-0d34-0410-b5e6-96231b3b80d8
The so-called "trivial implementation" has been with us for a few years now. It's probably safe to assume it works.. so remove the #if stuff


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@224147 91177308-0d34-0410-b5e6-96231b3b80d8