Revert "Fix the undefined-but-used odr-use marker (DR48)"

Wrong patch got committed (this one isn't ready for prime time).

This reverts commit r209996.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@209997 91177308-0d34-0410-b5e6-96231b3b80d8