Attempt to make test from r195886 portable with different shells

Windows and Hexagon complained. It's not clear which command is failing, so
will back out the changes if this doesn't do the trick.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195889 91177308-0d34-0410-b5e6-96231b3b80d8