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/unusedfields.cxx

@@ -193,7 +193,7 @@ void UnusedFields::run()
         for (const MyFieldInfo & s : definitionSet)
             output += "definition:\t" + s.access + "\t" + s.parentClass + "\t" + s.fieldName + "\t" + s.fieldType + "\t" + s.sourceLocation + "\n";
         std::ofstream myfile;
-        myfile.open( SRCDIR "/loplugin.unusedfields.log", std::ios::app | std::ios::out);
+        myfile.open( WORKDIR "/loplugin.unusedfields.log", std::ios::app | std::ios::out);
         myfile << output;
         myfile.close();
     }