Fix test to not write output to the test directory, as it may not be writable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217337 91177308-0d34-0410-b5e6-96231b3b80d8
Avoid writing to the test directory as it may not be writable.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217339 91177308-0d34-0410-b5e6-96231b3b80d8