[Zorg] Modify LIT flags for LibCXXBuilder.py

[EricWF]

Summary

I would like to add the --show-xfail and --show-unsupported flags to LIT within the LibCXXBuilder.
The extra output helps us keep track of the expected failures / unsupported tests without having to look through the entire log.

[EricWF]

Pushed as r216896.

zorg/buildbot/builders/LibCXXBuilder.py

             name='test.libcxx.new',
             command=[
                 properties.WithProperties('%(builddir)s/lit.venv/bin/lit'),
-                '-v',
+                '-v', '--show-xfail', '--show-unsupported',
                 properties.WithProperties(
                     '--param=cxx_under_test=%(cxx_path)s'),
                 '--param=use_system_lib=false',