Revert "Reverting r193835 due to weirdness with Go..."

The cgo problem was that it wants dwarf2 which doesn't support direct
constant encoding of the location. So let's add support for dwarf2
encoding (using a location expression) of data member locations.

This reverts commit r198385.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198389 91177308-0d34-0410-b5e6-96231b3b80d8