build: typo on config/Makefile.mingw64, msvc and msvc64.
    
    (Patch by Adrien Nader!)
    
    While trying to come up with the previous commit, I noticed that the
    various Windows config files had diverged: all but config/Makefile.mingw
    were lacking a '%' in a pattern and this prevents the pattern from matching
    anything.
    
    git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14176 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02