Revert "Fixed warning about visibility of field"

This reverts commit 65e7202947cafdbfe17ad7c25bb89ba4597241bc.

Did not really fix the warning
Reapplied workaround to fix dangling debug Value nodes on shutdown.

* Applied from here: https://codereview.chromium.org/10442019/
* Still occurs in LLVM 3.3 in some cases (not in benchmarks)