Fix Twine corruption problem with diagnostics.

This fixes the autobuilders I broke with a recent patch. Thanks echristo
and dblaikie for beating me with a clue stick.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220918 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed