Make this test not try to write on object file and test all of the
output rather than just part of it.

Also, remove the frighteningly ancient comment about not working with
the gcc-driver. (!!!)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187376 91177308-0d34-0410-b5e6-96231b3b80d8