Give lit a --xunit-xml-output option for saving results in xunit format
  
  --xunit-xml-output saves test results to disk in JUnit's xml format. This will allow Jenkins to report the details of a lit run.
  
  Based on a patch by David Chisnall.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223163 91177308-0d34-0410-b5e6-96231b3b80d8