The test runner does not rewrite instances of /dev/null inside the
quoted sh command. /dev/null does not exist, so opt will fail to open
it, and return a non-zero exit code.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173509 91177308-0d34-0410-b5e6-96231b3b80d8
