Revert "Partially revert r214761 that asserted that all concrete debug info...

Revert "Partially revert r214761 that asserted that all concrete debug info variables had DIEs, due to a failure on Darwin."

I believe this was addressed by r215157 and r215227, so let's have
another go at the bots, etc.

This reverts commit r214880.

llvm-svn: 215412