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/constantparam.py

@@ -13,7 +13,7 @@ def normalizeTypeParams( line ):
     return normalizeTypeParamsRegex.sub("type-parameter-?-?", line)
 
 # reading as binary (since we known it is pure ascii) is much faster than reading as unicode
-with io.open("loplugin.constantparam.log", "rb", buffering=1024*1024) as txt:
+with io.open("workdir/loplugin.constantparam.log", "rb", buffering=1024*1024) as txt:
     for line in txt:
         try:
             tokens = line.strip().split("\t")