b=393413

- set platform correctly for winxp

tools/buildbot-configs/testing/unittest/master.cfg

@@ -394,7 +394,7 @@ winxpFactory.addStep(CreateDir,
 winxpFactory.addStep(UpdateClobberFiles,
         cvsroot=CVSROOT,
         workdir='.',
-        platform='',
+        platform='winxp',
         logDir='..\\logs\\',
         env=MozillaEnvironments['vc8'])
 winxpFactory.addStep(MozillaClobberWin,