Fixed dangling file.

I think this is the correct way to fix a small issue of db70ebf
discussed in #980. Indeed, the file without cpp extension should stay there to avoid
data races, and be removed at the end.

This closes #980, please reopen if necessary

scripts/mklib.sh

@@ -64,7 +64,7 @@ do
     exit 1
   }
 
-  rm -f ${tmpfile} ${tmpfile}.bak
+  rm -f ${tmpfile} ${tmpfile}.bak ${tmpfile%.cpp}
   objs="$objs $obj"
 
 done