Support Unsupported Tests in xunit output

We were reporting  "Unsupported" tests in xunit as passes, however since
they are not run, it make more sense to mark them as skipped. The Junit
xml standard has support for that, so lets use it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332065 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed