put the loplugin output files in the workdir

so that the next time I accidentally leave one turned on, and commit it,
the buildbots will clean up naturally the next time they run 'make
clean'

Change-Id: Ia09dea9c272c322c7e2773c5458cb54aceb50dd1

compilerplugins/clang/finalclasses.py

@@ -7,7 +7,7 @@ definitionSet = set()
 inheritFromSet = set()
 definitionToFileDict = {}
 
-with open("loplugin.finalclasses.log") as txt:
+with open("workdir/loplugin.finalclasses.log") as txt:
     for line in txt:
         tokens = line.strip().split("\t")