[llvm][llvm-lit] Handle testsuite elapsed time being None

The time for all testsuites will always exist because lit
measures it itself. For a given testsuite, I guess that it
can be None if for example the suite is empty.

Author: DavidSpickett

llvm/utils/lit/lit/reports.py

@@ -114,7 +114,7 @@ def _write_testsuite(self, file, suite, tests):
                 skipped += 1
             if t.isFailure():
                 failures += 1
-            time += t.result.elapsed
+            time += t.result.elapsed or 0.0
 
         name = suite.config.name.replace(".", "-")
         file.write(