[lit] Speculatively fix PR24554 by manually closing the process handle

My theory is that somehow Python's refcounting and GC strategy isn't
closing the subprocess handle in a timely fashion.  This accesses the
private '_handle' field of the Popen object, but I see no other way to
do this. If this doesn't address the problem on the sanitizer-windows
buildbot, we can revert this change. If it does, then let's keep the
hack.

llvm-svn: 245946

llvm/utils/lit/lit/TestRunner.py

@@ -257,6 +257,9 @@ def executeShCmd(cmd, shenv, results):
     exitCode = None
     for i,(out,err) in enumerate(procData):
         res = procs[i].wait()
+        # On Windows, manually close the process handles.
+        if kIsWindows:
+            procs[i]._handle.Close()
         # Detect Ctrl-C in subprocess.
         if res == -signal.SIGINT:
             raise KeyboardInterrupt