Don't use 'exit' in lit script

Some buildbots use a shell that doesn't know 'exit'. So instead of using XFAIL
for UseAuto/iterator.cpp (since this problem doesn't exist for cmake) leave the
'grep' command and turn off the others.



git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@176295 91177308-0d34-0410-b5e6-96231b3b80d8