build: remove warning 32 (unused variable) in tools.
    
    (Patch by Adrien Nader!)
    
    Among other files, myocamlbuild_config.ml is built in this directory.
    This file defines many variables, most of which are not used and
    therefore trigger this warning which is then turned into an error
    through -warn-error A.
    build: remove warning 32 (unused variable) in tools.
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14169 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02