fix warnings when building openssl with the following compiler options:

        -Wmissing-prototypes -Wcomment -Wformat -Wimplicit -Wmain -Wmultichar
        -Wswitch -Wshadow -Wtrigraphs -Werror -Wchar-subscripts
        -Wstrict-prototypes -Wreturn-type -Wpointer-arith  -W -Wunused
        -Wno-unused-parameter -Wuninitialized