cannot assume that the current working directory is writable in all test
environments. I don't know a better way to write this test of hand, lets
discuss. Possibly, a better option would be to put these together with
other test testing the driver directly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@241885 91177308-0d34-0410-b5e6-96231b3b80d8